Open Tubular HPLC Columns Using Chemically Etched Poly(Tetrafluoroethylene) Serpentine Tubing

Abstract

A novel open tubular liquid chromatographic column has been developed and demonstrated. Narrow bore poly(tetrafluoroethylene) tubing was knitted into a serpentine configuration using an electronic breadboard as the supporting framework. Studies with unretained solutes showed that these tubes give much less band broadening per unit length than conventional capillary tubes of the same i. cl. due to enhanced radial mixing. When such tubes are treated with a sodium/naphthalene fluorocarbon etching reagent, a carbonaceous surface is formed on the inner wall which provides a stable chromatographic stationary phase. The resulting columns can exhibit either normal or reversed phase behavior, depending on the mobile phase used, and are amenable to both isocratic and gradient elution chromaitography.     

高效毛细管电泳分离机理的研究

应用色谱分离理论,综合考虑了分子扩散、进样量、电能消耗、电泳迁移等因素对高效毛细管电泳分离的影响,建立了高效毛细管电泳分离机理模型.以色氨酸为示踪样品进行实验,研究了电压、溶液浓度、进样量、毛细管管径等因素对理论板高度的影响,并与模型计算结果进行了比较.结果表明,本文所提出的模型能够较好地描述高效毛细管电泳的分离机理,该模型可作为优化操作参数和进行放大设计研究的基础.     

气固并流下行床气体扩散行为的研究

采用氢气稳态示踪方法在内径140mm的气固并流下行循环流化床中对气体扩散行为进行了实验研究.实验结果表明:下行床中气体扩散行为可用二维拟均相模型进行描述,其气体的径向扩散系数与气速、固体循环量及颗粒密度的关系可用下列准数关联式表示Pe_r=4.35×10_(-3)Re~(0.95)ε~(-73.4) 1>ε>0.99而下行床中气体轴向扩散系数要比提升管中小1个数量级以上.     

Diffusion and Permeation of Gases in Fiber-Reinforced Composites

Abstract

The presence of filler in a matrix phase greatly alters and also complicates the diffusion process, making experimental data very difficult to handle analytically. In this study both diffusion and permeability data were obtained in unfilled cellulose acetate films and cellulose acetate films filled with cheese cloth. Cheese cloth being highly permeable, the permeabilities and diffusivities of gases in the filled films are greater than in unfilled films due to reduced effective film thickness for molecular diffusion. A mathematical model has been developed which considers molecular diffusion to occur in that part of the film having no filler, while diffusion through the low-resistance cheese cloth is approximated by convective flow controlled only by the pressure gradient across the thickness of the cheese cloth yarn. The mathematical model predicts permeability values somewhat lower than experiment at low flow rates, but agrees well with experimental permeabilities at higher rates. The poor agreement between theoretical and experimental diffusivities is attributed mainly to errors involving the measurement of time lags. Morphological studies of the composite surfaces and cheese cloth filaments show that the cellulose acetate did not penetrate into the cheese cloth yarn which essentially retains its porous structure in the composite.     

Tracer Concentration Gradients for Diffusion Coefficients Exponentially Dependent on Concentration

A diffusion equation having a tracer diffusion coefficient exponentially dependent on solute concentration, D*=D₀* exp (β C ), was solved numerically for thin-film and thick-film boundary conditions and varying values of annealing time, film thickness, and β. For values of β in the range 3 to 10 mol fraction⁻¹, the calculated distribution of solute remained remarkably Gaussian. The apparent diffusion coefficient evaluated from such solute gradients was greater than the true tracer diffusion coefficient D ₀* by ≤20% for large β and shallow tracer penetration. The results were used to estimate possible errors in data which have been reported for several oxide systems, and may be used as a guide for the selection of experimental parameters so that corrections will not be necessary.     

Radial diffusion model for fragrance materials: Prediction and validation

A predictive model based on Fick's second law for radial diffusion is proposed and validated for modeling the diffusion of fragrance materials. A pure component, two binary systems, and a ternary system were used for validation. The model combines the prediction model to represent the liquid phase nonidealities, using the UNIFAC group contribution method, with the Fickian radial diffusion approach. The experimental headspace concentrations were measured in a diffusion chamber using the solid-phase microextraction technique and quantified using gas chromatography with a flame ionization detector. The numerical solutions were obtained along with an analytical model considering constant surface concentration. The odor intensities of the studied systems were calculated using Stevens' power law and the strongest component model, respectively. The numerical simulation presented good adherence to the experimental gas concentration data. The proposed methodology is an efficient and validated tool to assess the radial diffusion of fragrance and volatile systems.     

Texture Development and Microstructure Evolution in Liquid-Phase-Sintered α-Alumina Ceramics Prepared by Templated Grain Growth

Texture development in alumina that contains calcia and silica and has been templated with platelet-shaped α-Al₂O₃ particles has been evaluated. The texture fraction is shown to be related directly to template growth. Texture quality is controlled by the template concentration, decreasing at template concentrations of >10%, as a result of template–template interactions during tape casting. Almost fully textured alumina has been obtained at template concentrations of ≥20%. The growth of template grains is much more rapid in the radial direction and is shown to be inversely related to the thickness of the grain-boundary liquid. The activation energy for growth (376 kJ/mol) and the inverse relation with the grain-boundary thickness indicate that template growth in the radial direction is controlled by Al³⁺ diffusion.     

Sulfonation of solid polystyrene using gaseous sulfur trioxide

Kinetics of the heterogeneous sulfonation of polystyrene (PS) beads using gaseous SO₃ was investigated. Scanning electron microscopy (SEM) and electron diffraction scattering spectroscopy (EDS) was employed to study the kinetics of diffusion of SO₃ into the PS particles. The diffusion of SO₃ through the barrier of sulfonated polystyrene (SPS) on the beads surface was the primary parameter determining the rate and the yield of the sulfonation reaction. The measurement of the time dependence of the thickness of sulfonated layer formed on the solid PS surface provided for the hypothesis that the sulfonation in heterogeneous phase was diffusion controlled. Diffusion coefficients of SO₃ in PS at ?5°C, 22°C, and at 50°C and activation energy of SO₃ diffusion to the solid PS were determined from these experimental data assuming in the first approximation a simple diffusion unaffected by the ongoing sulfonation reaction. The experimental data were fitted using Johanson‐Mehl‐Avrami‐Jerofyeev‐Kolgomorov's equation to obtain an overall rate constant of heterogeneous sulfonation on solid PS surface. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers     

Strain effects in the mass flux of methanol in poly(methyl methacrylate)

Diffusion of organic solvents into glassy polymers often results in a phase transformation of the hard, solid polymer into a swollen, rubbery material. During the sorption, internal stresses exist in the swollen and glassy parts of the polymer and are thought to contribute significantly to the “anomalous” diffusion observed in many penetrant–polymer systems. In this investigation, isothermal sorption data for the methanol–poly(methyl methacrylate) system have been obtained on plates ranging in thickness from 1/32 to ¼ in. The results show features characteristic of both a strain-dependent diffusion coefficient and of a stress gradient contribution to the mass flux. An attempt to reproduce these results by combining a strain-dependent diffusion coefficient model with a stress-induced contribution to the flux is presented.     

Comparison of high-temperature gas chromatography and CO2 supercritical fluid chromatography for the analysis of alcohol ethoxylates

This work compares capillary supercritical fluid chromatography (SFC) and capillary high-temperature gas chromatography (HTGC) for the quantitative characterization of nonionic alcohol ethoxylate surfactants. Supercritical fluid chromatographic separations of the alcohol ethoxylates were obtained with a density-programmed carbon dioxide mobile phase and a fused silica capillary column. High-temperature gas chromatographic separations were obtained with a high-temperature polyimide-coated fused silica capillary column. In addition, a procedure was developed for the quantitation of the capillary chromatographic data using flame ionization molar response factors based on the effective carbon theory. The alcohol and ethoxylate distributions, mean molecular weights and average moles of the ethylene oxide are rapidly calculated from the chromatographic data. Advantages and limitations of SFC and HTGC procedures are illustrated and discussed. Based on this work, the following conclusions can be drawn: i) For routine quality control analyses of known alcohol ethoxylates, SFC and HTGC appear to be equally applicable. ii) SFC has the advantage of time because derivatization is not required, although derivatization does improve resolution. iii) HTGC has the advantage of resolving C₁₂ through C₁₈ alcohol ethoxylate oligomers, avoiding ambiguous identification of components. iv)SFC and HTGC both have disadvantages. SFC has a resolution limitation and HTGC discriminates against high molecular-weight components. Presented in part at the 83rd Annual Meeting in Chicago, IL, May 1991.     

Experimental and computational study on structure development of PMMA/SAN blends

Structure development in PMMA/SAN28 blends was studied experimentally with small-angle light scattering (SALS) and computationally with a diffuse-interface model based on the Cahn-Hilliard theory. All three stages of phase separation were observed with SALS. The diffusion coefficient was derived from the initial stage, while the evolution of the interface thickness was derived from all stages. The coarsening kinetics is more dominated by hydrodynamics in the late stage than in the intermediate stage of the phase separation. This is confirmed by the computational study which revealed that the coarsening becomes dominated by hydrodynamics when the capillary number is reduced from 10 to 0.5. A quantitative comparison between the experimental and numerically predicted phase separation kinetics is presented.     

Modelling of reactive stripping in monolith reactors

In this work, (reactive) stripping carried out in film flow monolith reactors developed for counter-current operation is investigated. Usually mass transfer in reactive separation has to be determined experimentally due to the complex flow patterns. However, monoliths have a simple geometry; only laminar flow is present throughout the column. This allows the calculation of the thickness of the liquid layer directly using Navier–Stokes equations. With this thickness known, the mass transfer can be calculated based on the convection in axial direction, diffusion in radial direction and vapour–liquid equilibrium. A model has been developed and implemented in Fortran^® based on the concept of a direct solution of convective diffusion equations, using the Thomas algorithm for solving the counter-current operation mode. Experimental data from literature have been used to validate the model for a binary and a multi-component system. The stripping of oxygen from saturated water by nitrogen was modelled assuming Fickian diffusion and vapour–liquid transfer based on the Henry constants. In a second step, multi-component diffusion and complex mass transfer at the interface were taken into account to describe the stripping of water by nitrogen from a mixture of hexyl-octanoate and cumene (solvent) under reactive stripping conditions.     

离子液体在色谱分析中的应用

综述了近年来国内外离子液体在色谱分析中的应用情况,主要包括离子液体用作气相色谱固定相,液相色谱流动相或流动相添加剂,以及毛细管电泳电解质、添加剂或涂布于毛细管壁上分离各种物质。     

Current advances in the non‐chromatographic fractionation and characterization of PEGylated proteins

For more than 30 years, PEGylation has been used to improve the physicochemical properties of several proteins and therapeutic drugs having a major impact in the biopharmaceutical industry. The purification of PEGylated proteins usually involves two basic challenges: (1) the separation of PEG‐proteins from other reaction products; and (2) the sub‐fractionation of PEG‐proteins on the basis of their degree of PEGylation and positional isomerism. Currently, most PEGylated protein purification processes are based on chromatographic techniques, especially size exclusion chromatography (SEC) and ion exchange chromatography (IEX). Nonetheless, other less frequently used strategies based on non‐chromatographic techniques such as ultrafiltration, electrophoresis, capillary electrophoresis, and aqueous two‐phase systems have been developed in order to fractionate and analyze PEGylated derivates. This review presents current advances in some of the most widely used non‐chromatographic strategies for the fractionation and analysis of PEG‐protein conjugates. Copyright © 2010 Society of Chemical Industry     

Bubble generation rules in microfluidic devices with microsieve array as dispersion medium

Microfluidic devices with microsieve array as the dispersion medium have been well recognized. However, few studies have been made on gas‐liquid two‐phase flow in microsieve dispersion devices. The bubble generation rules with single‐pore, radial‐array pores, axial‐array pores, and square‐array pores were systematically investigated. The rules of pore activation have been suggested by considering the capillary force, flow resistances of both dispersed phase and continuous phase. An empirical equation and a theoretical equation to predict the activation of pores in microfluidic devices were developed. An equation to correlate the average bubble diameter with parameter of channel structure, phase ratio, and Ca number of continuous phase was also developed. The strategy of design and scaling up for microsieve devices is proposed. Meanwhile, a device with dual‐size pores according to the rules derived is designed. This device achieved much better dispersion performance. © 2015 American Institute of Chemical Engineers AIChE J, 61: 1663–1676, 2015     

Quantitative characterization of dispersed particle size,size distribution,and matrix ligament thickness in polypropylene blended with metallocene ethylene–octene copolymers

The average rubber particle size, size distribution, and matrix ligament thickness between particles in polypropylene blends containing metallocene catalyzed ethylene–octene copolymers have been quantitatively analyzed, as functions of blend composition and phase viscosity ratio. Comparison has been made between experimental data and those predicted from a number of theoretical models. All blends showed two‐phase morphology, with interestingly a bimodal distribution of the rubber particle size. The ranges and averages of rubber particle size were mainly determined by blend composition and viscosity ratio between the phases, irrespective of comonomer content along the rubber chains. The logarithmic relationship between the matrix ligament thickness and rubber concentration was observed. The values of ligament thickness obtained from the experiments and theoretical models were not in agreement. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 2140–2149, 2001     

Diffusion of low‐molecular‐weight permeants through semi‐crystalline polymers: combining molecular dynamics with semi‐empirical models

A molecular dynamics‐based computational approach was used to study the diffusion of oxygen through a model semi‐crystalline polymer, namely linear low‐density polyethylene. The simulated molecules were validated by comparing the predicted properties with experimental values of available free volumes, on atomic scale, using positron annihilation lifetime spectroscopy and measured values of density. The semi‐crystalline polymer was considered as a composite network of a continuous amorphous phase and a dispersed crystalline phase. Based on this observation, the overall diffusion was simulated, including the diffusion through the crystalline phase, which has not been previously reported. A tight correlation was then achieved between experimental and simulated data by utilising several semi‐empirical and analytical models developed for composite materials. The proposed methodology in this work can be effectively used as a basis for designing polymer networks with controlled diffusion characteristics in a bottom‐up approach. © 2018 Society of Chemical Industry     

Asymmetry of Peak Shapes in Linear Gas—Liquid Chromatography

Abstract

A mathematical model describing axial dispersion, interparticle mass transfer, intraparticle gas diffusion, and diffusion in a uniform thickness liquid film is used systematically to investigate the influence of intraparticle diffusivity, diffusivity in a stationary liquid phase (SLP), partition coefficient, and thickness of liquid film on the shape of the peaks in linear gas—liquid chromatography by converting Laplace transformed equations into time domain. The low diffusivities of intraparticle and/or SLP can cause the asymmetry and long tail in chromatographic peaks. A higher partition coefficient and the film thickness at low diffusivities also give skewed peaks. At a higher mass transfer rate, the peak becomes sharper. From these results a guide can be suggested to avoid the asymmetric condition of long-tailing peaks.     

A parallel coextrusion technique for simultaneous measurements of radial die swell and velocity profiles of a polymer melt in a capillary rheometer

This article proposes a new experimental technique to simultaneously measure radial die swell and velocity profiles of polystyrene melt flowing in the capillary die of a constant shear rate rheometer. The proposed technique was based on parallel coextrusion of colored melt‐layers into uncolored melt‐stream from the barrel into and out of the capillary die. The size (thickness) ratio of the generated melt layers flowing in and out of the die was monitored to produce the extrudate swell ratio for any given radial position across the die diameter. The radial velocity profiles of the melt were measured by introducing relatively light and small particles into the melt layers, and the times taken for the particles to travel for a given distance were measured. The proposed experimental technique was found to be both very simple and useful for the simultaneous and accurate measurement of radial die swell and velocity profiles of highly viscous fluids in an extrusion process. The variations in radial die swell profiles were explained in terms of changes in melt velocity, shear rate, and residence time at radial positions across the die. The radial die swell and velocity profiles for PS melt determined experimentally in this work were accurate to 92.2% and 90.8%, respectively. The overall die swell ratio of the melt ranged from 1.25 to 1.38. The overall die swell ratio was found to increase with increasing piston speed (shear rate). The radial extrudate swell profiles could not be reasoned by the shear rate change, but were closely linked with the development of the velocity profiles of the melt in the die. The die swell ratio was high at the center (～1.9) and low (～0.9) near the die wall. The die swell ratio at the center of the die reduced slightly as the piston speed was increased. Polym. Eng. Sci. 44:1960–1969, 2004. © 2004 Society of Plastics Engineers.