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     

旋转填充床内高黏介质脱挥过程的传质模型(英文)

A mass transfer model for devolatilization process of highly viscous media in rotating packed bed(RPB) was developed based on penetration theory and mass conservation.Before establishing the model,some mass transfer experiments of thin film were conducted in a designed diffusion cell including vacuum and feeding system. In this study,acetone was used as the volatile organic compound(VOC) and syrup as the highly viscous media.The thickness of thin film was changed by using different liquid distributor.It was found that bubbling played an important role in the devolatilization.The correlation of diffusion coefficient of acetone in highly viscous dilute solution was proposed.The relative error between predicted and experimental data was within the range of ± 30% for diffusion coefficient of acetone in syrup.A comparison of experimental data of RPB with model indicated that the relative error was within ± 30% for efficiency of acetone removal.     

Kinetic Correlation for the Hindered Diffusion of Proteins in a Porous Packing Column*

Abstract Hindered diffusion of proteins in a porous packing plays an important role in proteinchromatographic purification.The HETP method was adopted to analyze the influence of axialdispersion, film mass transfer and hindered diffosion in the porous packing employing a size-exclusionchromatography(SEC)process.The retention behavior with eight proteins of different relativemolecular mass was experimentally detected with a commercial SEC column.A correlation basedon the relative molecular mass of the proteins and the packing porosity was developed and used topredict the effective diffusion coefficient of a protein in the Porous packing.The predicted valuesof effective diffusion coefficient were very consistent with the experimental results with the averageerror of 8.6%.     

Estimation of an effective water diffusion coefficient during infrared-convective drying of a polymer solution

This article deals with the drying of an aqueous solution of polyvinyl alcohol mixed with a plasticizer. A heating combining forced convection and short-infrared radiation was investigated. A one-dimensional model taking into account the shrinkage of the product was developed to get the temperature and moisture content evolutions during the drying. The water diffusion coefficient was estimated by an inverse method. A sensitivity analysis and numerical tests showed the relevance of using an objective function taking both mass and temperature measurements into account for the estimation procedure. This estimation was performed on several convective and infrared-convective experimental drying kinetics. The model predictions fit well mass and temperature experimental data. © 2009 American Institute of Chemical Engineers AIChE J, 2009     

An analytical method of estimating diffusion coefficients of gases in liquids from pressure decay tests

We present an exact solution of quasi-equilibrium model, based on pressure decay technique, to measure diffusion coefficient. The results of the quasi-equilibrium model are compared with the traditional equilibrium model and it was found that the latter is only a special case of former one. We provide new approximate solution to estimate diffusion coefficient that is more convenient to use, compared with the previously reported approaches. It also reveals that our solution is capable of taking into account greater portion of the collected pressure decay test data and is more accurate. Based on the developed solution, estimation approaches, including linear method and exponential method, are presented and applied to analyze synthetic and experimental pressure-decay data. The quasi-equilibrium model is also compared with the traditional equilibrium model. The results reveal that analysis of the test data using equilibrium model may introduce large error in estimation of diffusion coefficient. © 2018 American Institute of Chemical Engineers AIChE J, 65: 434–445, 2019     

用改进的基团贡献法计算二元体系液相分子扩散系数

一种改进的用基团贡献原理计算二元体系液相分子扩散系数的方法,可用于大部分非理想液相体系。用150多个体系的1000多个实验点对此方法进行了验证,结果表明对于理想体系和无限稀释溶液的分子扩散系数,计算值与实验值平均相对误差不超过5%,对于大部分的非理想体系其平均相对误差小于10%。与原有的经验、半经验关联式相比,改进的方法具有更大的适用范围,能更准确地预测液相分子扩散系数。     

有机分子在聚乙烯膜中扩散过程的分子动力学模拟

引言聚乙烯(PE)是由乙烯单体聚合而成的相对分子质量较高的线性烷烃,是合成树脂中应用最广泛的品种。扩散系数是描述传递现象的基本物性参数,在聚合物材料开发方面具有重要的理论特性和广阔的应用前景。用实验方法测定扩散系数时,操     

生物通风过程中的甲苯运移及生物降解

Bioventing is conducted on one-dimensional soil columns. A numerical model is developed for simulating the mass exchange, adivective and dispersive transport and biodegradation of toluene. The model parameters are estimated independently through laboratory batch experiments, or from literature. Simulations are found to provide reasonable agreement with experimental data. Experimental results show that toluene removal due to biodegradiation is more important at the later stage. The total cleanup time when NAPL (non-aqueous phase liquid) phase exists was twice more than that without NAPL. Sensitivity analysis of parameters suggests that model predictions are mainly dependent on mass transfer coefficient and microbial parameters, such as the half-saturation coefficient and maximum specific substrate utilization rate.     

The influence of molecular diffusion on mass transfer between turbulent liquids

The influence of molecular diffusion on liquid—liquid mass transfer in a stirred transfer cell has been found by measuring the rates transfer of helium and iso-butane from water to toluene and dekalin. These solutes have very different diffusion coefficients, their presence does not alter the physical properties of the liquids and, because their equilibrium distributions strongly favour the organic phases, the water phase mass transfer coefficient could be determined and was found to depend on the square root of the diffusion coefficient.The results are compared with the predictions of a model for liquid—liquid mass transfer under turbulent conditions, based on the approach of an eddy to the interface being restrained by interfacial tension and gravitational forces and taking into account eddy pressure fluctuations in both phases. This model provides a correlation for these results, as well as water phase mass transfer coefficients for the transfer of iso-butane from water to n-octanol, and previous stirred transfer cell results.     

生物通风过程中的甲苯运移及生物降解

Bioventing is conducted on one-dimensional soil columns.A numerical model is developed for simulating the mass exchange,advective and dispersive transport and biodegradation of toluene.The model parameters are estimated independently through laboratory batch experiments,or from literature.Simulations are found to provide reasonable agreement with experimental data.Experimental results show that toluene removal due to biodegradation is more important at the later stage.The total cleanup time when NAPL(non-aqueous phase liquid)phase exists was twice more than that without NAPL.Sensitivity analysis of parameters suggests that model predictions are mainly dependent on mass transfer coefficient and microbial parameters,such as the half-saturation coefficient and maximum specific substrate utilization rate.     

Mass transfer coefficients in a pulsed packed extraction column

The volumetric overall mass transfer coefficients have been measured in a pulsed packed extraction column using diffusion model for the toluene/acetone/water system. The experiments were carried out for both mass transfer directions. The effects of operational variables such as pulsation intensity and dispersed and continuous phases flow rates on volumetric overall mass transfer coefficients have been investigated. The experimental findings indicate that pulsation intensity and mass transfer direction have great influence on volumetric overall mass transfer coefficient. Significant, but weaker, are the effects of continuous and dispersed phase flow rates. The experimental results obtained in the present work are compared with some other types of extraction columns. Finally, two empirical correlations for prediction of the continuous phase overall mass transfer coefficient is derived in terms of Sherwood and Reynolds numbers. Good agreement between prediction and experiments was found for all operating conditions that were investigated.     

Estimation of concentration-dependent diffusion coefficient in drying process from the space-averaged concentration versus time with experimental data

The estimation of a concentration-dependent diffusion coefficient in a drying process is known as an inverse coefficient problem. The solution is sought wherein the space-average concentration is known as function of time (mass loss monitoring). The problem is stated as the minimization of a functional and gradient-based algorithms are used to solve it. Many numerical and experimental examples that demonstrate the effectiveness of the proposed approach are presented. Thin slab drying was carried out in an isothermal drying chamber built in our laboratory. The diffusion coefficients of fructose obtained with the present method are compared with existing literature results.     

Concentration-dependent diffusion of dye in adsorptive dyeing systems

A concentration-dependent dye diffusion model is extended in the present study to represent adsorptive dyeing systems. It is a revision of the previous one by incorporating the effect of external mass transfer resistance and concentration dependence of diffusion coefficient on the dye's diffusion process. The theoretical predictions using the extended model show excellent agreement with the observed data, significantly better than that of the previous one. It is also found that an adsorption equilibrium is achieved under most operating conditions due primarily to the fact that the dye diffusion within the pores is a considerably slower process than the dye adsorption.     

转盘式萃取塔有效扩散系数的预测及其在设计中的应用

A rotating disc column (RDC) with inner diameter 68 mm and 28 compartments is used in this study. Parameters including Sauter mean diameter, hold-up and mass transfer coefficient are measured experimentally under different operating conditions. The correlations in literature for molecular diffusion and enhancement factor equation including eddy diffusion, circulation and oscillation of drops are evaluated. A new equation for the effective diffusion coefficient as a function of Reynolds number is proposed. The calculated values of mass transfer co-efficient and column height from the previous equations and present equation are compared with the experimental data. The results from the present equation are in very good agreement with the experimental results, which may be used in designing RDC columns.     

数字全息干涉法测量液相质扩散系数的研究

介绍数字全息干涉法测量原理.设计并搭建基于数字全息干涉法和新的扩散槽测量质扩散系数的实验系统,并使用此系统测量了浓度为0.33 mol/l的KCl水溶液在温度为291.8、294.7、298.8、299.8、305.4、308.5、315.2 K条件下的质扩散系数,实验结果表明实验值和文献参考值之间相对偏差绝对值的平均数为1.3%,验证了试验系统的精确性和可靠性.最后,在此系统上测量了浓度为0.1 mol/1的蔗糖水溶液在288.15～338.15 K温度范围内的质扩散系数.为测量工程上急需新型燃料替代工质和新型制冷剂替代工质的质扩散系数提供了一种新的有效方法.     

葡萄糖水溶液扩散系数的测定与关联

液相扩散系数在化工数据中起着非常重要的作用,由于液体结构及扩散本身的复杂性,至今还没有一个合理的理论模型来预测液相扩散系数,有必要从实验和理论上对不同的体系进行研究.制备了金属膜池,用氯化钾溶液标定了膜池常数,并用已有可靠文献值的蔗糖水溶液验证了装置的可靠性.测定了298.15～328.15 K不同温度下葡萄糖水溶液的积分扩散系数,考察了温度对扩散系数的影响.在实验数据的基础上,提出一个有温度关联项的半经验模型,关联和计算了本实验的数据,结果与实验值吻合很好.     

分子体积对丙烯酸酯单体在PMMA中扩散系数的影响

根据Vrenta Duda自由体积扩散理论的推论 ,说明分子体积对扩散系数有指数性的影响关系 ;利用实验数据验证了该推论 ,得到了分子体积对扩散系数影响的简化模型为lgD2 =ξ2 1lgD1+2 331。这对研究梯度型聚合物光纤折射率梯度形成具有较重要的理论意义     

局部组成型的互扩散系数模型

根据局部组成概念建立了混合物中互扩散系数与自扩系数的关系,并以分子集团迁移的概念建立了混合物中组分的自扩散系数的预测方法,由此预测二元系的自扩散系数和互扩散系数与实验结果符合良好,比经典的Ｈａｒｔｌｅｙ模型有了很大地改进。     

Diffusion of a hydrocarbon mixture in a one-dimensional zeolite channel: An exclusion model approach

Zeolite channels can be used as effective hydrocarbon traps. Earlier experiments [K.F. Czaplewski et al., Micropor. Mesopor. Mater. 56 (2002) 55] show that the presence of large aromatic molecules (toluene) block the diffusion of light hydrocarbon molecules (propane) inside the narrow pore of a zeolite sample. As a result, the desorption temperature of propane is significantly higher in the binary mixture than in the single-component case. In order to obtain further insight into these results, we use a simple lattice gas model of diffusion of hard-core particles to describe the diffusive transport of two species of molecules in a one-dimensional zeolite channel. Our dynamical Monte Carlo simulations show that taking into account an Arrhenius dependence of the single-molecule diffusion coefficient on temperature, one can explain many significant features of the temperature programmed desorption profile observed in experiments. However, on a closer comparison of the experimental curve and our simulation data, we find that it is not possible to reproduce the higher propane current than toluene current near the desorption peak seen in experiment. We argue that this is caused by a violation of strict single-file behavior.