Coupled diffusion of water and ethanol in a polyimide membrane

In this work, the sorplion and steady state permeation of water‐ethanol mixture in an aromatic polyimidc membrane was investigated with the objective of revealing the coupling cherts of water and ethanol in their course of diffusion. The solubility of the watcr‐ethanol mixture in the membrane was determined by means of swelling‐distillation techniques. The sorption behavior was interpreted in terms of the thermodynamic equilibrium equations. The Maxwell‐Stefan mass transfer model was employed as a framework for modeling diffusion. Model equations derived therefrom enable us to cplculate coupled fluxes of water and ethanol from the experimental data. The coupling effects in the diffusion of water and ethanol were revealed by comparing the calculated coupled flux with non‐coupling flux, which was calculated by integration of the Fickian first law using independent diffusion coefficients. Furthermore, the implication of the sole adjustable parameter included in the derived model equations was discussed.     

Functional barriers in PET recycled bottles. Part I. Determination of diffusion coefficients in bioriented PET with and without contact with food simulants

A major outcome for recycled plastics consists of making food packaging materials. However, any contamination of collected plastics with chemicals may then be of concern for public health. A solution to mind migration is to use a layer of virgin polymer, named functional barrier, intercalated between the recycled layer and the food. This article aims to provide experimental values of diffusion coefficients (D) of model pollutants (surrogates) in poly(ethylene terephthalate) (PET) to be used for modeling migration through functional barriers. Diffusion coefficients of a large set of surrogates at low concentrations in PET were measured in various conditions. A solid‐to‐solid diffusion test was designed to avoid the use of a solvent that may induce plasticizing of the material and partitioning effects at the interface. Using [Log D = f(molecular weight)] correlations, the values of diffusion coefficients and activation energies of the surrogates measured by this method were shown to be consistent with the literature data obtained for gases, in permeation experiments, where no plasticization occurred. Migration from PET into food simulants was then studied. Migration into an aqueous medium is largely influenced by the solubility of the surrogates, the less soluble ones being not detected, despite high D values. With ethanol solvent, there were no partitioning effects, and the high plasticization effect of PET by ethanol considerably increases the apparent diffusion coefficients. The effects of temperature and plasticization on the relationship between diffusion coefficients and molecular weight are discussed. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2845–2858, 2004     

Parameters of gas dissolution in liquids obtained by isothermal pressure decay

A rapid and effective data analysis and interpretation approach is developed and validated for simultaneous determination of the film‐mass‐transfer and diffusion coefficients from time‐limited experimental data obtained by dissolving gas in liquids by the pressure‐decay method under isothermal conditions. Whereas previous approaches require experimental data until equilibrium and only determine the diffusion coefficient, accurate and rapid estimation of both parameters are achieved using a shorter set of time‐limited data, thereby reducing the errors owing to swelling by significant gas dissolution at later times. The equilibrium conditions can be predicted theoretically stemming from an analysis of the time‐limited data. This provides the estimates of the equilibrium pressure and gas solubility. This methodology not only yields accurate parameter values, but also alleviates the sufficiently large‐time collection of pressure‐decay data needed to essentially achieve equilibrium. © 2008 American Institute of Chemical Engineers AIChE J, 2009     

Diffusion of Saccharides and Sugar Alcohol Sorbitol in Chitosan Membranes and Beads

Diffusion coefficients of different sugars and the sugar alcohol sorbitol have been determined by two different experimental setups: mass transfer through a flat membrane in a diffusion cell and effusion experiments with beads in a batch stirred vessel. Diffusion experiments show highly consistent data with low uncertainties and high regression coefficients, while effusion experiments suffer from larger experimental uncertainties. For the diffusion through a chitosan membrane at 25 °C, typically one‐third of the free molecular diffusion coefficient is found, whereas at 40 °C only one‐quarter of it is reached. The influence of molecular size, structure, and temperature on the transport properties is discussed in detail.     

Effect of Temperature on Chiral Separation of Ketamine Enantiomers by High‐Performance Liquid Chromatography

Abstract

A semipreparative column packed with microcrystalline cellulose triacetate (MCTA) was used to separate ketamine enantiomers by high‐performance liquid chromatography (HPLC). The effect of temperature on the kinetics of mass transfer and equilibrium constants were evaluated by the moment analysis at 303, 313, and 323 K. Total porosity, bed porosity, and equilibrium constants were measured by the first moment. Pore diffusion and axial dispersion coefficients were evaluated by the second moment. It was observed that band broadening decreased with increasing temperature. The equilibrium constants were found to be greater than unity and decreasing with increasing temperature. The pore diffusion coefficients increased with increasing temperature and the main contribution to the band broadening was attributed to low mass transfer kinetics. The pore diffusion coefficients controlled the mass‐transfer process in MCTA column. These results may be used to the determination of operating conditions and computational simulation of a chromatographic separation in simulated moving bed unity.     

加压和超临界条件下乙醇分子的缔合

引言 在化学和化工领域,分子扩散系数是过程设计和装置优化所需的基本数据之一[1].乙醇作为一种高效绿色溶剂,具有良好的溶剂性能和比较温和的临界温度、临界压力(Tc=514.3 K,pc=6.38MPa),在食品、医药和化工等领域有巨大的应用空间[2].     

The Kinetics and Equilibrium of Ethanol Adsorption from Aqueous Phase Using Calcined (Na‐1,6‐Hexanediol)‐ZSM‐5

Na‐ZSM‐5, synthesized using 1,6‐hexanediol as the structure directing agent, has been found to have a suitable selectivity and adsorbing capacity for ethanol adsorption from aqueous solutions. In contrast to quaternary ammonium based Na‐ZSM‐5 zeolites, this Na‐ZSM‐5 did not show any catalytic interaction with ethanol during thermal desorption. The dynamics of the adsorption process were investigated using the finite volume “uptake rate” route. The data predicted from the governing relations of the process were correlated with experimental results. The micro‐diffusion coefficient was determined as a function of temperature.The macropore diffusional mass transfer contribution for biporous zeolite particles was found to be negligible.     

Fabrication of poly(lactic acid) films with resveratrol and the diffusion of resveratrol into ethanol

Poly(94% L ‐lactic acid) (PLA) films containing 0, 1, and 3 wt % resveratrol (PR0, PR1, and PR3) were extruded in a pilot‐plant scale blown‐extrusion machine. Yellow‐colored PLA films with reduced crystallinity were obtained, and the films absorbed UV‐visible light at 350–200 nm. The diffusion kinetics of resveratrol into ethanol at 9, 23, 33, and 43°C displayed Fick's behavior, and diffusion coefficients between 10⁻¹³ and 10⁻¹⁰ cm²/s were obtained. According to the Arrhenius equation, the energy of activation for the diffusion of resveratrol from PR1 and PR3 films was 175 and 177 kJ/mol, respectively. The temperature of diffusion had a stronger effect on the reduction of the weight average molecular weight of PLA than the processing conditions and the contact time with ethanol. However, diffusion of resveratrol was not affected by the degradation of PLA. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Type of polypropylene material significantly influences the migration of antioxidants from polymer packaging to food simulants during microwave heating

Three different polypropylene materials, polypropylene homopolymer (PP), propylene‐ethylene random copolymer (PP‐R), and propylene‐ethylene copolymer (PP‐C) are commonly used in plastic containers designed for microwave heating of food. Migration of antioxidants, Irganox 1010 and Irgafos 168, from PP, PP‐R, and PP‐C during microwave heating in contact with different food simulants was investigated by utilizing microwave assisted extraction (MAE) and high performance liquid chromatography (HPLC). The polypropylene material significantly influenced the migration rate, which decreased in the order of increasing degree of crystallinity in the materials. PP homopolymer was the most migration resistant of the studied materials especially in contact with fatty food simulants. The use of isooctane as fatty food simulant resulted in rapid depletion of antioxidants, while migration to another fatty food simulant, 96% ethanol, was much more limited. Migration to aqueous and acidic food simulants was in most cases under the detection limits irrespective of microwaving time and temperature. The diffusion coefficients were similar to what have been found previously under similar conditions but without microwaves. The effect of swelling was shown by the large increase in the calculated diffusion coefficients when isooctane was used as food simulant instead of 96% ethanol. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Self‐diffusion measurements of organic molecules in PDMS and water in sodium alginate membranes

The self‐diffusion of some organic molecules in silicone rubber and of water and water–ethanol mixtures in sodium alginate membranes was investigated to obtain information on the transport behavior in these systems. The temperature dependence of self‐diffusion was examined by the pulsed field gradient NMR technique. The experimental data confirm the homogeneous amorphous nature of PDMS and the affinity of silicone rubber to apolar solvents. The interrelations between solvent and polymer structures of the sodium alginate membrane varying the temperature have been obtained using differential scanning calorimetric. The results have been compared with the trend of self‐diffusion coefficients, and structure modifications of the membranes have been evidenced. The overall results confirm the potentialities of the technique used in measuring transport parameter in polymeric membranes. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 1119–1128, 1999     

Fixed bed modelling for acid dye adsorption onto activated carbon

The adsorption of three separate acid dyes onto activated carbon has been studied using fixed bed adsorption. A film‐pore diffusion model was developed and applied to the experimental breakthrough curve data. A sensitivity analysis showed that pore diffusion was the dominant mass transport mechanism. Pore diffusion coefficients were determined by an optimization routine with a minimization of the sum of errors squared. The external mass transfer coefficients were sensitive to the external fluid dynamic parameters, such as liquid flow rate and mean particle size. These fluid dynamic parameters did not affect the effective diffusion coefficient. The effective diffusion coefficient was not affected by changes in the fluid dynamic parameters but did change with differing initial dye concentrations. This may be due to a contribution from surface diffusion to the effective diffusion coefficient. Copyright © 2003 Society of Chemical Industry     

Mechanism of bubble formation in the drying of polymer films

A common problem in making thin polymer films by solution processing is the undesirable formation of bubbles during the drying process. These bubbles appear well below the boiling point of the solvent. Experience indicates, however, that the degassing of the polymer solutions reduces bubble formation, indicating a relationship with the presence of air. This work is based on a hypothesis that if the solubility of air in the polymer solution increases with solvent concentration, then the solution can become supersaturated with air as the concentration of the solvent is reduced during the drying process. To test this hypothesis the system poly(vinyl acetate)‐toluene‐nitrogen was chosen. Previously published data on the solubility and diffusion of nitrogen in the polymer‐solvent system were used. Different diffusion models based on the friction coefficients and free‐volume model were then used to correlate the diffusivity data so that the diffusion behavior of the ternary system can be predicted over a broad range of conditions. Finally, the thermodynamic and diffusivity correlations were incorporated into a multicomponent drying model which included main and cross‐diffusion terms to predict saturation behavior in the polymer solution during the drying process. The model without the cross‐diffusion terms represents the ideal system in which the diffusion of one component does not affect the diffusion of others. The drying model did not predict supersaturation of nitrogen when cross‐diffusion terms were neglected. Supersaturation of nitrogen was predicted, however, when the cross‐diffusion terms are included. Therefore, the cross‐diffusion terms in the mass transfer model are essential for the development of nitrogen supersaturation. Also different diffusion models based on the friction coefficients led to qualitatively similar predictions for the supersaturation of nitrogen. The simulation's results supported our experimental observations regarding bubble formation. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

A novel technique for local mass transfer measurements

A novel electrodeposition technique is developed to estimate time‐averaged convective local mass transfer coefficients. This method is based on the diffusion‐controlled deposition rate of copper. With an electrolyte solution consisting of H2SO₄ and CuSO₄, copper is dissolved at the anode and deposited onto the nickel cathode. The thickness of the copper, measured with an optical microscope, provides an estimate of the time‐averaged local mass transfer coefficient for the given location, and by depositing multiple layers, the coefficients under different flow conditions can be obtained from one cathode. The results for laminar flow in a smooth, round pipe showed good agreement with those calculated from the analytical Leveque solution. Results were also obtained for turbulent flow and demonstrate the potential for acquiring convective local mass transfer coefficients for various flow configurations.     

Modeling and Experimental Studies of Adsorptive Dewatering of Selected Aliphatic Alcohols in Temperature Swing Adsorption System

Based on experimental work, closely coupled with mathematical modeling, an analysis was performed of the adsorptive drying of selected water-aliphatic alcohol solutions. The experimental work involved ethanol, n-propanol, and n-butanol dehydration using two adsorbents, 3A and 4A zeolite molecular sieves. The isothermal model developed in this paper incorporates an overall linear mass driving force, including liquid film mass transfer and intraparticle diffusion coefficients, a variable axial diffusivity, and experimentally determined Langmuir-Freundlich isotherms. Breakthrough curves generated by the model were compared with those obtained experimentally, giving a fairly good fit. The model simulations enabled determination of the water content profiles in adsorbent beds.     

Diffusion of lignin macromolecules within the fibre walls of kraft pulp. Part I: Determination of the diffusion coefficient under alkaline conditions

The intrinsic rate of diffusion of soluble lignin from fibre walls to bulk liquor has never been determined previously because of experimental difficulties; for example, the diffusion rate determined in a stirred cell is affected by the mechanical action of stirring. In our work, the intrinsic rate of diffusion of lignin macromolecules from the fibre walls of a softwood kraft pulp was determined under alkaline conditions using a displacement cell which eliminated external heat and mass transfer resistances and pulp fibre disturbances. The effects of such experimental conditions as pulp bed height and liquid flow rate were studied. The diffusion rate can be described by a diffusion model for a hollow cylinder with a very wide range of diffusion coefficients. The diffusion rate increased with increasing pH. Our results provide a new understanding of the lignin diffusion process in fibre walls, which is affected by the size of lignin molecules and the pores, and by the electrostatic interactions between intrafibre pore walls and lignin.     

Dissolution mechanism of polymers in high pressure–high temperature n‐alkanes—Application to blends separation

The use of a high temperature–high pressure near critical solvent is an interesting alternative to dissolve high‐molecular‐weight polyolefins with alkanes. This characteristic allows their separation from the blends with other polymers. In the present work, the polymer dissolution of commercial polypropylene (PP) and polystyrene (PS) in n‐alkanes at high pressure and high temperature is analyzed. The comprehension of the different polymer dissolution behaviors and solvent affinities clarifies the understanding of the mechanism of PP/PS physical blend separation under these conditions. The PP dissolution in n‐pentane and n‐heptane was interpreted in terms of chain disentanglement and solvent diffusion. A mathematical model is proposed to predict the experimental results and to calculate mass transfer coefficients in order to quantify the PS barrier effects. It is possible to assess the effect of the temperature on the pure PP solubilization using these coefficients. In blends separation, it was demonstrated that the PS, insoluble at the same conditions, hinders the PP diffusion. As the PS blend content increases, the separation efficiency decreases. Particularly, mass transfer coefficient increases with PP content while PS is the matrix (PS barrier decreases). Afterwards, PP has no ulterior barriers and mass coefficient remains constant. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers     

超临界或高压CO2中无限稀释扩散系数的模拟

采用分子动力学模拟的方法对超临界二氧化碳的自扩散系数及甲醇和乙醇在超临界二氧化碳中的无限稀释扩散系数进行了模拟计算。结果表明,分子动力学模拟方法可较准确地反映二氧化碳的扩散性质,计算无限稀释扩散系数取得了与实验值较吻合的结果。采用这种新方法可以准确有效的地预测超临界体系的扩散性质,将会更加广泛应用于工程设计,因此分子动力学模拟作为先进的研究手段会得到越来越广泛的应用。     

Application of a New Gibbs Energy Equation to Model a Distillation Tower for Production of Pure Ethanol

A steady‐state equilibrium‐stage model based on MESH equations was proposed to simulate saline extractive distillation columns. The interaction parameters between each component of water‐CaCl₂ and ethanol‐water were obtained from mean ionic activity coefficients and vapor‐liquid equilibrium (VLE) experimental data. Additionally, the interaction coefficients for the ethanol‐CaCl₂ pair were fitted to experimental VLE data which were reported by Nishi for the ethanol‐water‐CaCl₂ system. It should be noted that adjustable parameters between each pair were considered to be temperature dependent. The results confirmed that the proposed model could accurately predict the experimental vapor‐liquid equilibrium data for ethanol‐CaCl₂‐water systems. Finally, the validated model was coded using MATLAB software and was solved using the Wang‐Henke method, including the VLE and enthalpy models.     

大孔吸附树脂HZ816对红霉素的固定床吸附过程研究

在上柱质量浓度为2.31—6.56 mg/mL、流量为14.33—42.80 mL/h的范围内研究了固定床吸附柱中大孔吸附树脂HZ816对红霉素的动态吸附过程,考察了原料液质量浓度和进口流量等操作参数对穿透曲线的影响。并采用基于液膜及孔内扩散模型的动力学模型,同时考虑吸附树脂颗粒内外扩散阻力及轴向扩散的影响,研究了固定床上红霉素在大孔吸附树脂中的吸附动力学,并从穿透曲线回归得到液膜传质系数孔内扩散系数。结果表明,在实验范围内,该模型能较好地描述红霉素在HZ816树脂上的吸附过程,由模型拟合得到的液膜传质系数随着原料液质量浓度减小而增大,随着流量升高而增大;孔内扩散系数随着原料液质量浓度增大而减小,随着流量升高而减小。为采用大孔吸附树脂HZ816吸附技术分离纯化红霉素工艺提供了实验和理论基础。     

Diffusion Studies of Glucose and Sucrose in Chitosan Membranes and Beads for Enzymatic Production Processes

The diffusion of glucose and sucrose was investigated in membrane and bead experiments. Concentration‐dependent diffusion coefficients of pure glucose and sucrose were determined in precipitated chitosan membranes of varying thickness using diffusion cell experiments. Contrary to fructose, the resulting diffusion coefficients of glucose and sucrose did not reach their free diffusion coefficients at infinite dilution suggesting additional interactions between chitosan and these two sugars. Counter‐diffusion in bead experiments showed a good agreement between predicted and measured data allowing the inclusion of the diffusion data in the simulation of the proposed production process for laminaribiose. In conclusion, the encapsulation in chitosan presented a good trade‐off between increased mass transfer resistance as evaluated by the Thiele modulus and improved thermal stability and antibacterial activity.