Adsorption with axial diffusion in shallow beds

Approach to constant pattern behavior and breakthrough behavior are analyzed for adsorption in fixed beds with axial diffusion. Local equilibrium between fluid and solid phases is assumed, with concentrations related by favorable Langmuir and Freundlich isotherms. Results are presented as midheight slopes of internal and actual breakthrough curves and as breadths of actual breakthrough curves. The solutions merge smoothly with asymptotic limits appropriate for deep beds and results obtained here for very short beds. It is shown that breakthrough curves are sharper than corresponding internal breakthrough curves for beds of any length, with the difference being even more pronounced in shallow beds than in deep beds. The principal factor that determines whether or not a breakthrough curve differs significantly from the corresponding internal breakthrough curve, regardless of whether the bed is long or short or the isotherm very favorable or linear, is the breadth of the adsorption wave near the bed outlet.     

Copper removal from effluents using a sulphonated lignite Bath and fixed-bed studies

Copper(ll) retention by a sulphonated lignite has been studied under equilibrium (adsorption isotherms) and dynamic (fixed-bed) conditions. Adsorption isotherms were fitted to the Langmuir equation from which saturation capacity and distribution coefficient for the sulpholignite were calculated. Breakthrough curves were determined and the overall mass transfer coefficients and exchange zone height were calculated from them. A model for the exchange mechanism is proposed.     

Fixed-bed adsorption with nonplug flow: Perturbation solution for constant pattern behavior

Adsorption of a dilute solute from a fluid in nonplug flow through a fixed bed is investigated via a perturbation approach. The continuity equation for fixed-bed adsorption with axial dispersion is solved for the constant pattern concentration profile with the axial velocity characterized by a general axisymmetric function and the system having no resistances to external or intraparticle mass transfer. The isotherm is slightly favorable (i.e., concave downward) in order to justify the assumption that axial gradients of concentration are independent of the radial coordinate in the bed, as in the classical problem of Taylor diffusion. A series expansion of a general isotherm is used to treat adsorption equilibrium. The solution reveals the formation of a radial gradient of fluid-phase concentration and breakthrough behavior at the bed outlet dependent on the nonlinearity of the isotherm and the magnitude of the nonplug-flow-velocity profile. The results can be used to predict the breadth of the breakthrough wave of many chromatographic-type processes for packed beds and slightly favorable isotherms.     

Isothermal adsorption in fixed beds

Prediction of single component adsorption in a packed bed operated isothermally is accomplished through the use of a mathematical model. The model accounts for the diffusional resistance between the bulk gas and the surface of the adsorbent particles, and for the diffusional resistance within the particles. The adsorption reaction within the pores is assumed to be very rapid compared to these two rate controlling mechanisms. The model can be used for isotherms of any shape and for gaseous feeds of any concentration. The partial differential equations of the model were solved numerically. Breakthrough curves are presented for four different isotherms and for two feed concentrations. The extension of the model to handle surface diffusion is treated. The model is compared with that of Rosen ≥^{11, 20} and the differences are discussed.     

端口夹角对气波引射器性能的影响和预测

端口夹角是影响气波引射器性能的重要结构参数。本文通过数值模拟和实验研究探讨了端口夹角对气波引射器性能的影响机理,并得出了装置最佳端口夹角的预测方法。气波引射器存在一个最佳的端口夹角ψopt：当端口夹角大于该值时,等熵效率明显下降;若端口夹角小于最佳值,中压压力小于极值中压压力时,等熵效率随夹角的减小稍有降低,中压压力大于极值中压压力时,等熵效率急剧下降。数值模型的计算结果与实验值相一致,本文所建数值模型可准确预测最佳端口夹角。入口气体状态恒定时,最佳端口夹角不随中压压力的变化而改变,随转速的增大而线性增大。上述结论对气波引射器的设计和性能优化具有指导意义。     

主喷嘴直径对蒸汽喷射器性能的影响

利用FLUENT软件对蒸汽喷射器复杂的内部流场进行数值模拟计算,并对喷射器内部流体流动过程中压力、速度等参数的变化规律进行分析研究,重点讨论了混合蒸汽压力和主喷嘴出口直径的变化对蒸汽喷射器引射性能的影响。结果表明：蒸汽喷射器存在一个临界出口压力,主喷嘴出口直径存在一个最优范围,此时喷射器的引射性能达到最佳,而且激波的耗散损失较小。     

Column Dynamics for Multicomponent Adsorption–Constant Pattern Formation

Abstract

A mathematical model for predicting adsorption breakthrough time for an N-component mixture from a carrier gas is described. Formation of constant pattern fronts is assumed, and the model accounts for roll-up of each species. Mixture equilibrium isotherms for all the species and length of the mass transfer zone, only for the least strongly adsorbed component, are needed for prediction.     

KINETICS OF ADSORPTION OF ORGANICS FROM WATER PRODUCED DURING IN SITU TAR SANDS EXPERIMENTS

The adsorption characteristics of dissolved organic matter onto activated carbon from tar sand product waters were investigated in this study. Equilibrium isotherms obtained at 278 and 298  K were nonlinear over the entire liquid concentration range. Breakthrough curves were obtained in packed bed experiments as a function of bed length, particle size, and liquid velocity. The breakthrough curves were analyzed to establish the relative importance of the various individual mechanisms that contributed to the overall adsorption process.     

ADSORPTION OF ORGANICS FROM A TRUE IN-SITU OIL SHALE RETORT WATER ON ACTIVATED CARBON IN PACKED BEDS

The adsorption of a true in-situ oil shale retort water on activated carbon at 278 and 298 K was studied in batch experiments and in packed beds with continuous liquid flow. The isotherms were nonlinear over the liquid concentration 0 to 875 mg/1. Breakthrough curves were obtained in packed bed experiments as a function of bed length, particle size, and liquid velocity. A differential approach was used to calculate the mass transfer coefficients and the rates of adsorption. Also the breakthrough curves were analyzed to establish the relative importance of the various individual mechanisms that contributed to the overall adsorption process.     

ADSORPTION OF ORGANICS FROM A TRUE IN-SITU OIL SHALE RETORT WATER ON ACTIVATED CARBON IN PACKED BEDS

The adsorption of a true in-situ oil shale retort water on activated carbon at 278 and 298 K was studied in batch experiments and in packed beds with continuous liquid flow. The isotherms were nonlinear over the liquid concentration 0 to 875 mg/1. Breakthrough curves were obtained in packed bed experiments as a function of bed length, particle size, and liquid velocity. A differential approach was used to calculate the mass transfer coefficients and the rates of adsorption. Also the breakthrough curves were analyzed to establish the relative importance of the various individual mechanisms that contributed to the overall adsorption process.     

Extension of the linear driving force-dusty gas model approximation to include surface or micropore diffusion

This paper presents linear driving force approximations for the dusty gas model in a bisolute system obeying linear or Langmuir isotherms, in two situations: when there is a nonnegligible surface flux in parallel with the diffusive and convective fluxes; and when there is a micropore resistance to mass transfer in series. The approximations were developed using a semi-empirical procedure that starts with the particle response to a square wave perturbation considering a simple diffusion/convection mechanism, and proceeds by consecutive corrections to this basic result. These corrections are obtained using superposition, similarity and pattern recognition. The approximations are good (average quadratic error ⩽10%) when representing the system cyclic steady state, whether the perturbations are sharp or smooth.     

Simplified Predictions of Breakthrough Fronts for Constant-Pattern Adsorption and Ion Exchange

Abstract

The loading cycle of many (perhaps most) commercial adsorption and ion exchange operations involves a favorable isotherm. Concentration fronts for favorable isotherms approach a constant pattern for long bed lengths, and most industrial adsorption and ion exchange operations use sufficiently deep beds that the constant-pattern conditions are approached. Once a constant pattern is established, the region around the front can be analyzed using conventional methods developed for continuous absorption/stripping operations, but the location of the feed and withdrawal points must be assumed to move down the bed at the same rate at which the front moves. Using this approach, the constant-pattern front can be calculated for any shape of constant-pattern isotherm. The dimensionless distance in the bed is expressed in terms of transfer units, and the shape of the front can be evaluated graphically even when the relations can not be integrated analytically. This procedure is illustrated for binary ion exchange isotherms. In the simplest cases, exchange of ions with like charge, the integration can be performed analytically. For other cases, numerical and graphical solutions are illustrated.     

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.     

Adsorption of Imazamox herbicide onto Filtrasorb 400 activated carbon

Imazamox is an imidazolinone herbicide, a new class of pesticides, which can exist as cationic, anionic or neutral species in water. The adsorption isotherms of Imazamox onto Filtrasorb 400 (F400) activated carbon were determined varying the pH and the ionic strength of the aqueous medium. The results show that ionic strength has no significant effect on Imazamox uptake, contrary to pH, and that F400 has a high affinity for Imazamox. Moreover, it is found that Imazamox adsorbs onto F400 as its neutral form. The best fit of the experimental points is obtained with the Langmuir–Freundlich model, consistent with surface site heterogeneity. Finally, calculating Langmuir–Freundlich isotherms for various constant pH values, it is shown that the two plateaus observed in the experimental isotherms obtained at free pH are due to the variation of the pH along the isotherms.     

Removal of Acid Dyes from Aqueous Solutions using Chemically Activated Carbon

Abstract

Textile dyes (Acid Yellow 17 and Acid Orange 7) were removed from its aqueous solution in batch and continuous packed bed adsorption systems by using thermally activated Euphorbia macroclada carbon with respect to contact time, initial dye concentration, and temperature. The activated carbon was prepared using a cheap plant-based material called Euphorbia macroclada, which was chemically modified with K₂CO₃. Lagergren-first-order and second-order kinetic models were used to fit the experimental data. Equilibrium isotherms were analyzed by Langmuir and Freundlich isotherms. Equilibrium data fitted well the Langmuir model in the studied temperature (25–55°C) ranges. The maximum adsorption capacity of AY17 and AO7 onto activated carbon was found to be 161.29 and 455 mgg^?1, respectively by Langmuir isotherm at 55°C. Breakthrough curves for column adsorption have also been studied. The desorption of dyes has been experimentally investigated using NaOH solution of pH 11.     

Moisture Equilibrium Isotherms for a Commercial Liquid Package Paper

Moisture equilibrium isotherms are very important in drying and storage processes analysis. So, the DEQ/UEM process separation group is building a data bank for cellulose, paper, and textile isotherms and their fit with available literature equations. In this context, the experimental isotherms of a brazilian specific commercial paper, the KLABIN-PR KLAPAK commercial liquid package paper were obtained. The experimental equilibrium data were obtained by exposing the material to different ambient conditions of temperature and relative humidity controlled by the use of saline solutions. The samples were placed in glass flasks left inside an oven to provide a better adjust of temperature conditions, being periodically weighed until constant weight. KLAPAK moisture equilibrium isotherms were built from the obtained experimental results and temperature effects on its behavior were analyzed. Then, these results were fitted with the help of some models and equations available from literature.     

Skin resistance for adsorbate mass transfer into extruded adsorbent pellets

Mass transfer resistances for adsorption of nitrogen from a binary gas mixture containing 79% N₂+21% O₂ were measured on three samples of extruded mordenite pellets by analysing the breakthrough curves from an adiabatic column. An adiabatic constant pattern model with Linear Driving Force mass transfer mechanism was used for data analysis. It was found that the three samples exhibited significantly different mass transfer resistances despite the fact that their particle sizes and pore structures were similar and the equilibrium isotherms for adsorption of nitrogen and oxygen on these materials were identical. This implied that the resistance to mass transfer existed in an impervious skin at the surface of the extrudates. Scanning electron micrographs of the materials confirmed the existence of a skin barrier. Pure gas and binary nitrogen and oxygen adsorption isotherms on the zeolite were measured at various temperatures. They could be described adequately by the Langmuir model.     

沼气调峰用LNG混空装置的设计与测试

针对沼气产气量不稳定的问题,提出了采用LNG气化掺混空气作为沼气调峰气源的解决方案,设计并加工了一种LNG引射空气混合器,模拟生产实际对引射混合器的运行特性进行了实验研究。结果表明在引射器出口压力一定时,混气比(空气:天然气)随着进口压力的增加而显著提升;进口压力一定时,混气比随着出口压力的增加而逐渐减小;考虑进出口压力对混气比的共同作用时,提高进口压力,混气比随出口压力升高而降低的趋势减缓;提高出口压力,混气比随进口压力升高而上升的趋势加剧。为获得与沼气发酵罐相同的出口压力,引射器进口压力应为0.25 MPa。