基于矩法和时间域分析法研究稠密CO2中甲苯和对氯苯在硅胶固定床系统中的吸附和传递性质

Based on chromatographic theory, the moment method and the time-domain fitting analysis were applied to measure and evaluate the adsorption equilibrium constant and mass transfer properties (axial dispersion coefficient and effective intra-particle diffnsivity) for toluene and p-dichlorobenzene on silica gel adsorbent in the subcritical and supercritical CO2. An apparatus based on supercritical fluid chromatography was established and the experiments were performed at temperatures of 298.15-318.15 K and pressures of 7.5-17.8 MPa. The two methods have been compared. The results show that for the systems studied here the moment method can give reasonable values for both adsorption equilibrium constant and mass transfer properties, but the time-domain analysis only can obtain the adsorption equilibrium constant. The dependence of adsorption equilibrium constant and mass transfer properties on temperature and pressure was investigated.     

脉冲超声对固定床中1300树脂吸附栀子甙吸附性能的影响(英文)

The effects of pulse ultrasound with different pulse parameters on the breakthrough curves of Geniposide on Resin 1300 were studied. The mass transfer model describing the adsorption process was constructed. Adsorption capability and the overall mass-transfer coefficient were obtained by fitting the constructed mass-transfer model and the experimental data. The effects of pulse ultrasound on adsorption of Geniposide on Resin1300 in a fixed bed were studied and compared. Amount of Geniposide adsorbed on Resin 1300 in the presence of ultrasound is lower than that in the absence of ultrasound, but the mass-transfer rate with ultrasonic irradiation is higher than that without ultrasound. Furthermore, mass transfer rate is enhanced by pulse modulation. In the conditions studied, the adsorption equilibrium constant decreases with increasing ultrasonic power, while the overall mass-transfer co-efficient increases. With increasing pulse duty ratio, adsorption equilibrium constant decreases initially, reaches a minimum when pulse duty ratio is 0.5, and then increases. On the contrary, the overall mass-transfer coefficient in-creases initially and reaches a maximum when pulse ratio is 0.5, and then decreases. Effects of pulse period on ad-sorption equilibrium and mass transfer rate reached the peak at pulse period of 28.6 ms.     

气体在临界温度附近吸附行为的实验研究

Adsorption equilibria of CH4 and N2 on activated carbon and silica gel were measured for a wide temperature rang covering the critical point:158-298K for CH4,and 103-298K for N2.The determination of the compressibility factor is shown to have considerable effect on isotherm behavior at conditions after the isotherm maximum.A change in adsorption mechanisms on crossing the critical temperature was observed in all cases. The kind of adsorbents and how far the equilibrium temperature to the critical one are major factors affecting the transition of isotherms from sub-to supercritical.All continuous isotherms can be modeled by a unique model for the supercritical region.The satisfactory fitting of the model to the experimental isotherms proved the reliability of the absolute adsorption determined by the proposed method.     

超临界流体中反应速率常数与密度的相互关系

A new method,which correlates rate constants of chemical reactions and density or pressure in supercritical fluids,was developed.Based on the transition state theory and thermodynamic principles, the rate constant can be reasonably correlated with the density of the supercritical fluid,and a correlation equation was obtained. Coupled with the equation of state (EOS) of a supercritical solvent,the effect of pressure on reaction rate constant could be represented.Two typical systems were used to test this method.The result indicates that this method is suitable for dilute supercritical fluid solutions.     

基于单气泡非稳膜机理的相际传质模型

A gas-liquid mass transfer model based on an unsteady state film mechanism applied to a single bubble is presented. The mathematical model was solved using Laplace transform to obtain an analytical solution of concentration profile in terms of the radial position r and time t. The dynamic mass transfer flux was deduced and the influence of the bubble size was also determined. A mathematical method for deducing the average mass transfer flux directly from the Laplace transformed concentration is presented. Its accuracy is verified by comparing the numerical results with those from the indirect method. The influences of the model parameters, namely, the bubble size R, liquid film thickness δ, and the surface renewal constant s on the average mass transfer flux were investigated. The proposed model is useful for a better understanding of the mass transfer mechanism and an optimum design of gas-liquid contact equipment.     

Adsorption equilibrium of citric acid from supercritical carbon dioxide/ethanol on cyano column

Supercritical adsorption equilibrium has a significant role in defining supercritical adsorption behavior. In this paper, the adsorption equilibrium of citric acid from supercritical CO2/ethanol on a cyano column was systemat-ical y investigated with the elution by characteristic point method. Equilibrium loading was obtained at 313.15 K and 321.15 K with supercritical CO2/ethanol densities varying from 0.7068 g·cm?3 to 0.8019 g·cm?3. The exper-imental results showed that the adsorption capacity of citric acid decreased with increasing temperature and in-creasing density of the supercritical CO2/ethanol mobile phase. The adsorption equilibrium data were fitted wel by the Quadratic Hill isotherm model and the isotherms showed anti-Langmuir behavior. The monolayer satura-tion adsorption capacity of citric acid is in the range of 44.54 mg·cm?3 to 64.66 mg·cm?3 with an average value of 56.86 mg·cm?3.     

基于实验等温线确定超临界气体绝对吸附量的数学方法

A mathematical method was proposed for the determination of absolute adsorption from experimental isotherms. The method is based on the numerical equality of the absolute and the excess adsorption when either the gas phase density or the amount adsorbed is not quite considerable. The initial part of the experimentalisotherms, which represents the absolute adsorption, became linear with some mathematical manipulations. The linear isotherms were reliably formulated. As consequence, either the volume or the density of the supercritical adsorbate could be determined by a non-empirical way. This method was illustrated by the adsorption data of supercritical hydrogen and methane on a superactivated carbon in large ranges of temperature and pressure.     

基于多场协同理论的渗透蒸发传质模型

Toprovide a theoretical basis for optimizing the pervaporation procedure, a mass transfer model for pervaporation for binary mixtures was developed basedon the multi-fields synergy theory. This model used the mechanism of sorption-diffusion-desorption and introduced a diffusion coefficient, which was dependent on the feed concentration and temperature. Regarding the strong coupling effect in the mass transfer, the concentration distribution in membrane was predicted using the Flory-Huggins thermodynamic theory. The batch experiments and other experiments with constant composition-were conducted-using a modified chitosan pervaporatioffmembrane to separate tert-butyl alcohol （TBA）-water mixtures. The parameters of the mass transfer model were obtained from the flux of the experiments with a constant composition and the activity coefficients available through phase equilibrium equation, using the Willson equation in the feed side and the Flory-Huggins thermodynamic theory within the membrane The simulation results of the experiments .are in good agreement with the results, of the experiments.     

Adsorption equilibrium for Z-ligustilide on C18-bonded silica from supercritical carbon dioxide

Adsorption equilibrium is of great importance for the preparative supercritical fluid chromatography(pre-SFC) in defining supercritical adsorption behavior and the industrial amplification.This paper presents adsorption isotherms of Z-ligustilide from supercritical carbon dioxide(SC-CO_2) on C18-bonded silica.Adsorption behavior was studied at 305.15 K,313.15 K and 323.15 K with SC-CO_2 density varying from 0.687 g·cm~(-3) to0.863 g·cm~(-3) with the elution by characteristic points(ECP) method.The adsorption amount of Z-ligustilide from SC-CO_2 on C18-bonded silica decreased with the increasing density of the mobile phase as well as the increasing temperature.Adsorption equilibrium data were fitted by Langmuir and Freundlich isotherm models,and the Langmuir isotherm model performed better for describing the whole adsorption process on the column.The monolayer saturation adsorption capacity of Z-ligustilide is in the range of 3.0 × 10~(-4) mg·cm~(-3) to5.5 × 10~(-4) mg·cm~(-3) with an average value of 4.0 × 10~(-4) mg·cm~(-3).     

Mass transfer area in a multi-stage high-speed disperser with split packing

In this study, the mean droplet diameter in the cavity zone and the total mass transfer area of a multi-stage highspeed disperser(HSD) reactor with different packing combinations were measured and evaluated. The effects of rotational speed and packing radius, as well as the packing ring radius and numbers, on the mean droplet diameter and the total mass transfer area were evaluated. A model was established to calculate the mass transfer area in the cavity zone in the HSD reactor, and it was found that the packings contribute 61%–82% of the total mass transfer area. A correlation for predicting the mass transfer area in the packing zone was regressed by the dimensionless analysis method. An enhancement factor based on the mass transfer area in the packing zone was proposed to evaluate the effect of packing combination on mass transfer area. Two optimum packing combinations were proposed in consideration of the mean droplet diameter and the enhancement factor.     

Chromatographic Analysis of Limonene and Linalool on Silica Gel in Supercritical Carbon Dioxide

ABSTRACT

Adsorption behavior of limonene and linalool, which are respectively the principal constituents of terpene and oxygenated compounds in citrus oil, on silica gel in the presence of supercritical carbon dioxide was analyzed by the tracer response method. In this study a two-column system was used to eliminate the effect of nonideal behavior at the sample injection. Adsorption equilibria and mass transport properties were evaluated by means of the moment method at pressures of 8.8–23.5 MPa and temperatures of 313–333 K. The adsorption equilibrium constant was larger for higher temperature and lower pressure when linalool was selectively adsorbed on silica gel. The apparent heat of adsorption ranged from –20 to 230 kj/mol. The Peclet number and the ratio of intraparticle effective diffusivity to molecular diffusivity were 0.013–0.257 and 0.002–0.716, respectively.     

Dynamic analysis of adsorption equilibrium and rate parameters of reactants and products in MTBE,ETBE and TAME production

Adsorption equilibrium constants of ethanol, methanol, isobutylene, isoamylenes (2M2B, 2M1B), MTBE and TAME on Amberlyst 15 catalyst were evaluated from the packed bed moment technique. Adsorption equilibrium constants of alcohols were found to be two orders of magnitude greater than the adsorption equilibrium constants of i-olefins and the corresponding tertiary ethers. However, their apparent heat of adsorption values are quite low (-6,7 kJ/mol and ?8.3 kJ/mol for methanol and ethanol, respectively). Among the i-olefins, isobutylene gave the highest adsorption equilibrium constant and the heat of adsorption (-54.2 kJ/mol The adsorption equilibrium constant of 2M2B on a catalyst, which was pretreated with ethanol, was about three times greater than the corresponding value obtained on fresh catalyst. Second moment analysis indicated that diffusion resistance in both macropores and microspheres of the catalyst are equally significant.     

Impulse Response Analysis for Adsorption of Ethyl Acetate on Activated Carbon in Supercritical Carbon Dioxide

Abstract

Adsorption equilibria and mass transport properties for ethyl acetate on activated carbon have been evaluated in the presence of supercritical carbon dioxide by means of the impulse response technique. A two-column system, one for dissolving solute and one for adsorption, was used to evaluate the phenomena purely in the adsorption column. The adsorption equilibrium constant was larger for higher temperature and lower pressure. The apparent heat of adsorption calculated from the temperature dependence of the adsorption equilibrium constant was 30–40 kJ/mol. The intraparticle effective diffusivity was larger for higher temperature and lower pressure. The Peclet number that relates to the axial dispersion coefficient was 0.08–0.39. These estimated parameters are in good agreement with those obtained from desorption measurements reported in the literature.     

ADIABATIC SORPTION OF BULK SINGLE ADSORBATE FROM AN INERT GAS-EFFECT OF GAS-SOLID MASS AND HEAT TRANSFER COEFFICIENTS

The effects of the gas-solid mass and heat transfer coefficients on the dynamics of adiabatic adsorption of a single adsorbate exhibiting Type I behavior were analyzed by numerically solving the conservation equations for a column. It was assumed that the adsorbate obeyed Langmuir equilibra and the local mass transfer rate could be described by the linear driving force model. The properties of the front zones were found to be controlled by mass transfer, while those of the rear zones were primarily determined by heat transfer. The separation between the two zones might vanish under certain conditions resulting in overlap of the two zones. The front zones were found to be constant pattern. The rear zones can be constant or proportionate pattern depending on the equilibrium properties and the feed condition of the adsorbate.     

ADIABATIC SORPTION OF BULK SINGLE ADSORBATE FROM AN INERT GAS-EFFECT OF GAS-SOLID MASS AND HEAT TRANSFER COEFFICIENTS

The effects of the gas-solid mass and heat transfer coefficients on the dynamics of adiabatic adsorption of a single adsorbate exhibiting Type I behavior were analyzed by numerically solving the conservation equations for a column. It was assumed that the adsorbate obeyed Langmuir equilibra and the local mass transfer rate could be described by the linear driving force model. The properties of the front zones were found to be controlled by mass transfer, while those of the rear zones were primarily determined by heat transfer. The separation between the two zones might vanish under certain conditions resulting in overlap of the two zones. The front zones were found to be constant pattern. The rear zones can be constant or proportionate pattern depending on the equilibrium properties and the feed condition of the adsorbate.     

CR型吸附剂对蔗糖和还原糖的吸附特性

本文提出液相色谱技术测定吸附相平衡常数和传质系数参数的估值模型，测定蔗糖还原糖在碱土金属型的ＣＲ型吸附剂上的吸附相平衡常数和总传质系数。结果表明：吸附相平衡常数随温度的升高而下降，吸附剂的选择性也随之下降；液固相间的总传质系数随温度的升高而增大，并随流速的增大而增大。在三种ＣＲ型吸附剂中，ＣＲ－２型吸附剂有较好的传质动力学性能和对还原糖吸附有较大的选择性。     

EPA和DHA在超临界流体色谱柱中的传质动力学

用超临界流体色谱 (SFC)法研究了EPA和DHA在C18上的吸附和传质性能 .建立了色谱动力学模型并获得了模型参数 ,较好地拟合了实验流出曲线 .结果表明吸附平衡、轴向弥散、流体相传质和颗粒内有效扩散都是影响SFC分离EPA和DHA的重要因素     

Modelling high pressure extraction processes

Semibatch flow extraction of oil and other active ingredients from some plant materials (Silybum marianum, pepper, paprika and cocoa) with supercritical fluids (SCF) such as CO₂ and propane at different operating conditions was studied. Dynamic behaviour of the extraction runs was analysed by a mathematical model based on the adsorption–desorption equilibrium of extractable component from solid tissue, the diffusion of extractable component dissolved in SCF to the surface and mass transfer through the external film into the bulk. The linear driving force concept was employed to incorporate intraparticle diffusion as well as external mass transfer. Results show that the simplified model, which describes desorption process at equilibrium, could successfully describe cumulative rate data and is specially interesting for observation of the cross-over effect for adsorption–desorption, i.e. how desorption is changed with the increase of temperature at constant pressure.     

External and internal mass transfer effect on photocatalytic degradation

A rational approach is proposed in determining the effect of internal and external mass transfer, and catalyst layer thickness during photocatalytic degradation. The reaction occurs at the liquid–catalyst interface and therefore, when the catalyst is immobilized, both external and internal mass transfer plays significant roles in overall photocatalytic processes. Several model parameters, namely, external mass transfer coefficient, dynamic adsorption equilibrium constant, adsorption rate constant, internal mass transfer coefficient, and effective diffusivity were determined either experimentally or by fitting realistic models to experimental results using benzoic acid as a model component. The effect of the internal mass transfer on the photocatalytic degradation rate over different catalyst layer thickness under two different illuminating configurations was analyzed theoretically and later experimentally verified. It was observed that an optimal catalyst layer thickness exists for SC (substrate-to-catalyst) illumination.     

DYNAMIC ANALYSIS OF SORPTION OF VOLATILE ORGANIC COMPOUNDS IN WATER

Chlorinated and brominated volatile organic compounds are among the groundwater pollutants creating major environmental problems. In this study, dynamic behavior of certain volatile organic compounds in water was investigated by using a novel moment technique. Adsorption equilibrium constant and the penetration length of tracers were evaluated by the first absolute and the second central moment expressions derived for a pulse-response system. In order to obtain adsorption equilibrium constant and penetration length, pulse-response experiments were carried out with different tracers in a one-sided adsorption cell at 30°C. The adsorption equilibrium constants at the gas-water interface were calculated for 1,2-dichloroethane, 1,1,1-trichloroethane, and carbon tetrachloride. This study showed that the adsorption equilibrium constant and the penetration length values could be successfully evaluated using the one-sided adsorption cell moment technique. The adsorption equilibrium constant for 1,2-dichloroethane, 1,1,1-trichloroethane, and carbon tetrachloride were found to be 0.30, 0.49, and 0.54 cm³/cm², respectively.