活性炭纤维吸附填充床突破曲线预测(Ⅰ)精确解与近似解

针对活性炭纤维吸附填充床,当吸附等温方程为线性时,考虑轴向弥散、纤维内扩散以及纤维外对流传质阻力,获得了阶跃进样时突破曲线的精确解以及拟对数概率密度函数近似解和二次方近似解。并在讨论模型参数对突破曲线影响的同时,对精确解和两种近似解进行了比较。结果表明,在较宽的模型参数范围内,两种近似解与精确解均吻合较好,但二次方近似解复杂,计算困难;而拟对数概率密度函数近似解简单,计算方便。     

活性炭纤维吸附填充床突破曲线预测(Ⅱ)实验及模型的验证

实验测定了活性炭纤维填充床吸附水中微量铅离子的突破曲线和吸附等温平衡数据,研究了活性炭纤维填充床的吸附性能。应用活性炭纤维吸附填充床突破曲线的精确解和两种近似解对实验数据进行了模拟。结果表明,本实验条件下理论计算值与实验数据均吻合较好;简单、计算速度快的拟对数概率密度函数近似解适用于模拟活性炭纤维填充床突破曲线;由突破曲线实验数据可方便准确地估算平衡常数;活性炭纤维吸附填充床内轴向弥散对突破曲线有较大影响,是不可忽略的因素。     

活性炭纤维填充床脱除水中苯酚及填充床的再生

采用活性炭纤维吸附法净化水中微量的苯酚。在25℃、30℃和35℃下，实验测定活性炭纤维吸附苯酚的吸附平衡等温线，该吸附等温线符合Langmuir型，最大饱和吸附容量达0．26kg(苯酚)／kg(活性炭纤维)在25℃下；0．25kg(苯酚)／kg(活性炭纤维)在30℃下；0．239kg(苯酚)／kg(活性炭纤维)在35℃下。水溶液的pH值将影响吸附容量，在碱性条件下吸附容量显著下降，这将有利于吸附剂的再生。苯酚在活性炭纤维填充床的穿透曲线被测量，在5％突破点处的动态吸附容量为0．14kg(苯酚)／kg(活性炭纤维)在25℃下。采用40℃、5％NaOH溶液再生被苯酚饱和的活性炭纤维填充床，再生后吸附效率达90％以上。     

活性炭填充床脱除水中苯酚及填充床的再生

实验研究了活性炭填充床脱除水中苯酚的吸附性能,探讨其饱和吸附填充床的再生方法,结果表明当平衡浓度范围为0－0．8kg/m^3时,活性炭对水中苯酚的吸附能力达230kg/kg（吸附剂）,吸附等温线符合Langmuir型,填充床的穿透曲线和穿透时间强烈依赖于实验条件,较高的进料浓度,较大的进料速度,以及较短的床层长度都将使填充床穿透较快;用热的NaOH稀溶液可再生被苯酚饱和的活性炭纤维填充床,再生效率达90％以上。     

氯苯酚在活性炭纤维上吸附平衡的研究

研究了水溶液中氯苯酚在活性炭纤维上的吸附平衡,实验探讨了反应温度、溶液pH值对活性炭纤维吸附平衡的影响。实验结果表明,平衡吸附量随着温度降低而升高;当pH值<7时,平衡吸附量几乎不随溶液的pH值而变化,而当pH值>7时,氯苯酚在活性炭纤维上的平衡吸附量随着pH值的增加而减小,pH值愈大,平衡吸附量减小的愈快。分别采用Langmuir模型和Freundlich模型描述吸附平衡等温线,在实验范围内Langmuir模型与实验数据吻合较好。     

间歇吸附器内活性炭纤维吸附性能

为研究活性炭纤维的吸附性能,针对纤维状吸附剂,建立了间歇吸附模型并推导出当吸附等温方程为线性时该模型的解析解。用活性炭纤维吸附水中微量三氯甲烷实验对模型进行了验证。实验测定了间歇吸附器内水中微量三氯甲烷的主体浓度变化曲线及吸附等温平衡线,通过比较主体浓度变化曲线与模型计算值,由误差等值图法估算了有效扩散系数以及液膜传质系数。     

苯酚在活性炭上的吸附与脱附研究

本文研究了苯酚水溶液在活性碳上的吸附平衡关系,溶液ｐＨ值对活性炭吸附性能的影响,苯酚在固定床上的吸附动力学和脱附动力学。同时采用间歇法和固定床连续法研究吸附苯酚后的活性炭碱再生工艺过程,多次再生对活性炭再生效率的影响,探讨了碱法再生活性炭的初步规律。     

Fe2O3-AC吸附剂对水中对硝基苯酚的吸附动力学研究

对Fe改性活性炭制得Fe2O3-AC吸附剂,并用于对硝基苯酚废水处理;通过静态试验方法研究所制备吸附剂对水溶液中对硝基苯酚的吸附等温和吸附动力学过程。结果表明,Fe2O3-AC吸附剂对废水中对硝基苯酚的吸附过程符合Langmuir等温方程,对硝基苯酚最大吸附量可达286.4 mg/g,内扩散不是吸附过程唯一的控制步骤,准2级动力学模型能更好的反映Fe2O3-AC吸附剂对对硝基苯酚的吸附机理。     

水中丙酮在活性炭上吸附平衡与动力学研究

研究了水中丙酮在活性炭上的吸附平衡与动力学曲线,对在20、30、40℃下的吸附等温线用Freundich方程拟合,得出了满意的结果。选择合适的实验条件,在消除了外膜阻力的条件下,表明颗粒内扩散中的表面扩散占主要地位,考察了初始浓度、温度、活性炭粒径等因素对丙酮吸附的影响,并用间歇搅拌槽吸附的表面扩散模型拟合出扩散时间常数。     

苯酚在活性炭纤维上的吸附平衡及动力学研究

利用活性炭纤维（ACF）吸附法处理含苯酚模拟废水,通过间歇静态吸附,测定了室温下苯酚初始浓度及吸附剂质量对吸附性能的影响。结果表明,Freundlich模型能较好地描述该吸附等温过程,苯酚在ACF表面发生多分子层物理吸附;苯酚由溶液主体传递到ACF表面为传质控制步骤。利用超声碱洗方式再生饱和吸附剂,再生后ACF对苯酚吸附容量保持较好。     

Biosorption of the Reactive Blue 5G Dye in a Fixed Bed Column Packed with Orange Bagasse: Experimental and Mathematical Modelling

The removal of reactive dye in a fixed bed column packed with orange bagasse was modelled using a model that considers the effects of axial dispersion, external and internal mass transfer limitations, and the equilibrium in the liquid-solid interface. The equilibrium and kinetic parameters were obtained through fit the model to the experimental data. In the parameters identification procedure the PSO optimization method was used. The mathematical model showed good performance when describing the dye adsorption process. Furthermore, orange bagasse is an attractive and cost-effective alternative as an adsorbent to remove reactive blue 5G dye from wastewaters.     

Study of the Fixed‐Bed Adsorption Behavior of Phenylalanine on Solvent Impregnated Resins,Part III

Abstract

The implementation of the SIR technique for the amino acid separation from diluted aqueous solutions in a fixed‐bed column is presented and a mathematical model for the prediction of the adosrption behavior is developed. Independently determined equilibrium and kinetic parameters are used for the calculation of the breakthrough curves. Fixed‐bed parameters, such as axial dispersion and bed porosity, are determined experimently and compared with correlations. Analysis of the Biot and Bodenstein number reveal that the mass transfer through the film liquid around the particles, as well as the axial dispersion in the column, could be neglected at the studied experimental conditions. A simplified mathematical model was found to give the best prediction to the experimental breakthrough curves over a wide range of feed concentrations and flow rates.     

Mathematical modeling and simulation of steady state plug flow for lactose-lactase hydrolysis in fixed bed

A detailed mathematical model for evaluating lactose hydrolysis with immobilized enzyme in a packed bed tubular reactor is presented. The model accounts for axial and radial dispersion effects, chemical reaction and external mass transfer resistances but is void of significant internal diffusion resistances of the particles. The comprehensive model was then simplified to a plug flow model for lactose-lactose hydrolysis in fixed bed. The resulting plug flow model was solved by using Runge-Kutta-Gill method via employing different kinetics for lactose hydrolysis. The reliability of model simulations was tested using experimental data from a laboratory packed bed column, where the β-galactosidase of Kluyveromyces fragilis was immobilized on spherical chitosan beads. Comparison of the simulated results with experimental exit conversion show that the plug flow model incorporating Michaelis-Menten kinetics with competitive product (galactose) inhibition are appropriate to interpret the experimental results and simulate the process of lactose hydrolysis in a fixed bed when the mass transfer resistance was reduced by a factor of 34.5.     

LIQUID PHASE TRANSPORT PROPERTIES IN A HIGH PRESSURE PACKED COLUMN

A mathematical model of fluid flow and mass transfer in a packed bed was derived and used to evaluate the liquid phase axial dispersion and mass transfer coefficients under high pressure conditions. The least-squares method was used to evaluate the rate parameters from experimental breakthrough curves, and the agreement between the concentration curves predicted from rate parameters and those measured experimentally was good. Experiments were performed at 20 and 200°C with water as a solvent and nonporous soda-lime glass beads as packing. Although the axial dispersion coefficient was independent of temperature and pressure, the mass transport parameters were found to be pressure dependent.     

A 3-zone model for protein adsorption kinetics in expanded beds

The adsorption behavior of expanded beds is more complex than that of fixed beds, since the adsorbent particle size, local bed voidage and liquid axial dispersion will vary axially with expanded height. Models applicable to fixed beds maybe not adequately describe the hydrodynamic and adsorption behavior in expanded beds. In this paper, a 3-zone model is developed, in which the model equations are written for the bottom zone, middle zone, and top zone of the column, respectively, and the model parameters, such as the adsorbent particle diameter, bed voidage and liquid axial dispersion coefficient, are zonal values. In-bed breakthrough curves are predicted by the 3-zone model, and tested against literature data for lysozyme adsorption on Streamline SP in an expanded bed.Model parametric sensitivity is analyzed. The effects of film mass transfer resistance, liquid axial dispersion and adsorbent axial dispersion on the breakthrough curves are weaker than that of protein intraparticle diffusion resistance for stable expanded beds. Adsorbent particle size axial distribution and bed voidage axial variation significantly affect in-bed breakthrough curves, therefore, model parameters should not be assigned uniform values over the whole column; instead the model should account for the adsorbent particle size axial distribution and bed voidage axial variation.     

Study on mass transfer of ethyl acetate in polymer adsorbent by experimental and theoretical breakthrough curves

A new polymeric adsorbent with highly hypercrosslinked structure was developed for the removal of VOCs from polluted air. The purpose of this work is to obtain the intraparticle mass transfer coefficient of the adsorbent particles. Adsorption experiments for obtaining breakthrough curves were carried out with a fixed bed system. A dynamic mathematical model for the fixed bed adsorption system was developed. By model fitting, the overall mass transfer coefficient was determined when the deviation error was minimum. Then, the intraparticle mass transfer coefficient of the adsorbent was determined when the external mass transfer resistance was eliminated at higher velocities. Furthermore, a linear relationship of the intraparticle mass transfer coefficient and equilibrium coefficient at lower inlet gas concentrations range was correlated. Moreover, an equation for predicting external mass transfer coefficient at low Reynolds number range at room temperature was obtained.     

Adsorption fixed beds modeling revisited: Generalized solutions for S-shaped isotherms

Adsorption fixed bed models are of paramount importance in chemical and environmental engineering research. Although the related literature is rich, the vast majority of models employed are either phenomenological, based on chemical reaction kinetics, or limited to systems that obey simple equilibrium isotherms (favorable, unfavorable, linear, and rectangular) combined to linear driving force (LDF) for the solid-phase mass transfer kinetics and ideal plug flow. This paper complements the existing studies by presenting and analyzing a versatile nondimensional fixed bed model equipped with diffusion-based mass transfer kinetics and nonideal flow terms and adapted to deal with S-shaped (sigmoidal) isotherms. A discussion is conducted on the rather unusual fixed bed dynamics produced by systems that follow S-shaped isotherms, a subject which has been rarely and nonsystematically discussed in the related literature. Thus, this study aims at providing better understanding of the interactions of S-shaped isotherms, mass transfer, and axial dispersion on the shape of adsorption fixed bed breakthrough curves and comes to clarify and complement previously published results, especially on the unexplored effects of the isotherms’ inflection point on the breakthrough curves.     

THE IMPORTANCE OF AXIAL DISPERSION IN LIQUID-PHASE FIXED-BED ADSORPTION OPERATIONS

Methods are given for computing concentration profiles and breakthrough curves in fixed bed adsorbers for Freundlich and Langmuir equilibria, for cases of zero and non-zero axial dispersion. The methods are limited to situations in which either particle diffusion or external film diffusion is the dominant mass transfer process. By considering parameter values typical of liquid phase systems, it is shown that the values of parameters representing the ratios of mass transfer resistances to the axial dispersion coefficient serve as indicators of whether or not axial dispersion effects are important. Axial dispersion can be significant whenever the particle size and/or flow rate is substantially smaller than usual.     

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.