海藻酸纤维对水溶液中Fe~(3+)的吸附动力学研究

以海藻酸纤维作为吸附材料研究了纤维对水溶液中Fe3+的吸附性能,用准一级动力学方程、准二级动力学方程、Elovich方程、粒子扩散方程、双常数方程和指数函数方程数学模型对不同Fe3+浓度、吸附时间的吸附曲线进行分析,研究了其吸附的动力学机理。结果表明:在研究的浓度和条件范围内,准二级动力学模型、Elovich方程和双常数方程的拟合度较好,模拟值与实验值吻合较好,说明海藻酸纤维吸附Fe3+是复杂的非均相扩散的化学吸附过程。粒子扩散方程表明颗粒内扩散不是控制海藻酸纤维吸附Fe3+过程的唯一步骤,而是由膜扩散和颗粒内扩散联合控制。     

Sorption dynamics in fixed‐beds of inert core spherical adsorbents including axial dispersion and Langmuir isotherm

The effects of axial dispersion and Langmuir isotherm on transient behavior of sorption and intraparticle diffusion in fixed‐beds packed with monodisperse shell‐type/inert core spherical sorbents are studied. The system of partial differential equations of the mathematical model is solved numerically using finite difference methods. Results are presented in the form of breakthrough curves for adsorption and desorption processes. Results reveal that the shape of the breakthrough curves is influenced by both hydrodynamic and kinetic factors. Hydrodynamic factor is governed by axial dispersion and is controlled by changes of Peclet number. Simulation results reveal that when linear adsorption isotherm is used, the effect of axial dispersion on breakthrough curves of the system is important for Peclet numbers smaller than 50, whereas, for Langmuir isotherm axial dispersion is considerable for Peclet numbers less than 80. In addition, effects of type of adsorption isotherms and size of adsorbents on breakthrough curves are investigated, and results are compared with existing reports in the pertinent literature. © 2009 American Institute of Chemical Engineers AIChE J, 2009     

Adsorption behavior of cationic dyes on citric acid esterifying wheat straw: kinetic and thermodynamic profile

The kinetic and thermodynamic behaviors of cationic dye adsorption onto citric acid esterifying wheat straw (EWS) from aqueous solution were investigated. Two cationic dyes, methylene blue (MB) and crystal violet (CV) were selected as adsorbates. The kinetic and thermodynamic parameters of dye adsorption were examined with a batch system by changing various experimental factors (e.g. initial pH, EWS dosage, dye concentration, contact time, temperature). The MB and CV removal ratios came up to the maximum value beyond pH 4. The 2.0 g/L or up of EWS could almost completely remove MB and CV from 250 mg/L of dye solution. The adsorption percentages of MB and CV kept above 95% over a range from 50 to 350 mg/L of dye concentration when 2.0 g/L of EWS was used. The isothermal data followed the Langmuir model. The adsorption processes could be described by the pseudosecond-order kinetic model. The dual linear plots of intraparticle diffusion indicated that two intraparticle diffusion steps occurred in the dye adsorption processes. The thermodynamic study indicated that the adsorptions of dyes were spontaneous and endothermic. High temperatures favored the adsorption processes.     

Adsorption and mass transfer characteristics of metsulfuron-methyl on activated carbon

Removal of a synthetic organic herbicide, metsulfuron-methyl (MSM), from aqueous solutions has been studied in batch and stirred tank adsorbers charged with granular activated carbon particles. Two kinetic parameters, film mass transfer and intraparticle diffusion coefficients, were estimated from concentration decay curves obtained in the batch adsorber. Based on these kinetic parameters, the concentration profiles measured in the stirred tank adsorber were simulated. From experimental and simulated results, it was proven that the film mass transfer at external surfaces of carbon particles controls the overall mass transfer, particularly at low mixing (rotation of blades), during the adsorption of MSM by granular activated carbon particles.     

Heterogeneous catalysis rate parameters in a gradientless reactor by the method of moments

The transient behaviour of an internally-recycled catalytic reactor has been studied accounting for the contributions from intraparticle diffusion, adsorption and surface reaction. Equations for the zeroth, first and second absolute moments of the break-through curves are given in terms of the rate constants for the three elementary steps (first order processes are assumed throughout). The moments can be obtained from experimental break-through curves and the rate parameters for adsorption and surface reaction then evaluated from such data. Simplified equations also are derived for the case of insignificant chemical reaction and this case is used to test the method experimentally. Values of the hydrogen adsorption equilibrium constant for γ-alumina supported Co Mo-Ni catalyst are reported.     

DETERMINATION OF MASS TRANSPORT PARAMETERS FOR FIXED-BED ADSORBERS

An innovative technique has been developed for determination of external (“film”) and internal (“intraparticle”) mass transport parameters associated with uptake of solutes by porous solids in fixed-bed adsorbers. These parameters are required for predictive modeling of the dynamics of such systems as activated carbon columns and ion exchange beds. Current methods for evaluation of film transfer coefficients and effective intraparticle diffusivities involve correlation procedures and separate batch-reactor measurements of adsorption rates, respectively. These methods frequently introduce and compound significant errors in subsequent predictive modeling Tor full-scale process design. The present work develops a method by which, on the basis of the characteristics of breakthrough curves measured in specially designed micro-columns, more accurate and reliable simultaneous determinations of both film transfer coefficients and effective surface diffusivities can be done. Verification of the procedure is demonstrated by the agreement of predictions generated from a mathematical model, in which mass transfer coefficients determined from the micro-column technique are used, with experimental breakthrough data for larger scale adsorbers.     

Kinetic evaluation of phenol/aniline mixtures adsorption from aqueous solutions onto activated carbon and hypercrosslinked polymeric resin (MN200)

Kinetic adsorption of phenol and aniline from aqueous solution onto activated carbon and hypercrosslinked polymeric resin MN200 were evaluated in single and binary system. Larger phenol and aniline uptakes were observed for activated carbon in single as well as binary system, which can be attributed to the better physical properties of activated carbon, for instance larger surface area and micropore area. The kinetic experimental data was properly fitted by the pseudo-first and pseudo-second-order rate equations. A synergetic effect between solutes was observed since phenol and aniline sorption kinetic in binary system was faster than the individual sorption of each solute in single system, as well as a slight increase in the kinetic parameters obtained in binary system. The particle diffusion rate was defined as the rate limiting mechanism in the singles and binary system for phenol and aniline kinetic adsorption on both adsorbents. Two steps were markedly defined by the Weber and Morris intraparticle diffusion analysis for phenol and aniline onto both adsorbents. In binary systems, the intraparticle diffusion was influenced by the physical properties of adsorbents.     

在Pt／Al2O3催化剂上气相苯加氢反应的动力学

在研制得到了高活性和高选择性 Pt/Al_2O_3催化剂的基础上,采用微反-色谱联用装置考察了气相苯加氢反应的动力学。假定在催化剂表面上存在着两种不同的活性中心,一种吸附氧;另一种吸附苯、环己烷及反应中间物,并假定吸附氢与吸附苯间的表面反应为过程的控制步骤,从而导出动力学方程。通过实验测得了不同反应条件下的反应速率和组分分压,并用非线性回归方法处理实验数据,求得方程中各参数。通过偏差分析、方差分析及 Boudart 提出的四条判断准则,验证了动力学模型及回归参数的合理性。结果得到了此动力学模型与实验数据较好地吻合。在此基础上测定了反应的活化能及氢、苯和环已烷的吸附热。     

Application of silica gel/polyaniline composite for adsorption of ascorbic acid from aqueous solutions

Silica gel and a chemically modified silica gel with polyaniline (PAN) were used for adsorption of ascorbic acid (AA) from aqueous solutions. The surface morphology of the adsorbents was studied by scanning electron microscopy (SEM). Adsorption experiments were carried out using both batch and columnar systems. In batch system, the effects of some important parameters such as sorbent dose, contact time, initial concentration and temperature of the adsorbate were studied. Based on regression analysis, the sorption data obtained for SiO₂ were best represented by Freundlich isotherm and for the PAN/SiO₂ composite, the equilibrium sorption data were fitted better by Langmuir isotherm. The kinetic studies showed that the adsorption of AA on both sorbents follows pseudo second-order kinetics which implies a chemisorption mechanism and according to diffusion model, intra-particle diffusion is the rate-controlling step. The thermodynamic studies also showed that PAN/SiO₂ is a more effective adsorbent to adsorb AA than an unmodified SiO₂. In columnar mode, the effects of salt on breakthrough curve were investigated. Two kinetic models, Thomas and Adams–Bohart, were applied to experimental data to predict the breakthrough curves using linear regression and determine the characteristic parameters of the column. Error analysis was carried out to investigate the adequacy and accuracy of the model equations. Desorption study showed that the adsorbed ascorbic acid is readily eluted from the column using dilute solution of NaOH. PAN/SiO₂ was found to be a promising solid phase adsorbent to preconcentrate ascorbic acid from aqueous solutions and subsequent analysis.     

Removal of Organic Impurities from Polymer Pellets

An investigation into the behavior of removing low molecular organics from polymer pellets in a countercurrent extraction column is presented. A mathematical model is developed, describing it in terms of intraparticle diffusion, adsorption, interphase equilibrium, convection and dispersion. The corresponding parameters are determined using nonlinear regression. The resulting partial differential equations are solved using a numerical method. The validity of the model is verified by means of experimental data.     

Adsorption of pollutants on to activated carbon in fixed beds

The adsorption of certain pollutants, namely phenol, p-chlorophenol, sodium dodecyl sulphate and mercuric ions, on to activated carbon has been studied using fixed bed systems. There are three main methods of contacting in solid/liquid adsorption systems, namely batch, fixed bed and fluidized bed systems. In fixed bed adsorption the adsorption rate is determined on the basis of adsorption equilibrium (unfavourable, linear, favourable or completely irreversible) and the controlling mechanism (external film mass transport, internal pore diffusion, internal solid phase diffusion or longitudinal diffusion). One or more of the previous transport mechanisms may be rate controlling depending on the solute-adsorbent system. For an adsorbent like activated carbon which is highly porous both external transport and pore diffusion will be very important. An adsorption model, based on external mass transport and internal pore diffusion, has been applied to the systems to predict theoretical breakthrough curves. These curves have then been compared with experimental data and using a ‘best fit’ technique, an effective pore diffusion coefficient can be determined for each sorbate–carbon system.     

交联海藻酸钠固定化的腐殖酸多孔性薄膜对铀(Ⅵ)的吸附性能及机理

采用戊二醛交联海藻酸钠固定化的腐殖酸,制备得到多孔性薄膜(GA-HA/SA),用于去除含铀废水中的铀(Ⅵ)。通过静态吸附实验,研究了pH值、初始浓度、接触时间、温度对GA-HA/SA吸附U(Ⅵ)效果的影响,进行了吸附过程的热力学与动力学分析;通过红外光谱(FTIR)、扫描电镜(SEM)、X射线能谱(EDS)探讨了相关吸附机理。实验结果表明,pH值为6时吸附效果最好,吸附在60 min基本达到平衡。吸附过程符合Langmuir和Dubinin-Radushkevich(D-R)等温模型;25℃时,最大吸附容量为312.5 mg·g^-1。吸附动力学过程符合准二级速率方程(R² >0.99),吸附速率的控速步骤为颗粒内扩散。GA-HA/SA对U(Ⅵ)的吸附是自发的吸热反应。SEM-EDS、FTIR和D-R模型分析结果表明,与U(Ⅵ)相互作用的基团主要是羧基,且GA-HA/SA吸附U(Ⅵ)的机理表现为离子交换。     

Study of equilibrium,kinetic and thermodynamic parameters about methylene blue adsorption onto natural zeolite

Adsorption equilibrium and kinetic of methylene blue (MB) onto natural zeolite was studied in a batch system. Variables of the system include contact time, pH, salt concentration, temperature, and initial MB concentration. The increase in temperature resulted in a higher MB loading per unit weight of the zeolite. Langmuir, Freundlich, Redlich–Peterson, Koble–Corrigan and Temkin isotherm models were applied to experimental equilibrium data of MB adsorption depending on temperature. The effect of contact time at different temperatures and initial concentration were fitted to pseudo-second-order kinetic model. Linear regressive method and nonlinear regressive method were used to obtain the relative parameters. The error analysis was conducted to find whether linear method or nonlinear method was better to predict the experimental results and which model was better to fit the experimental data. Both methods were suitable to obtain the parameters. The Redlich–Peterson equation was best to fit the equilibrium data. The pseudo-second-order kinetic model can be used to describe the adsorption behavior. The nonlinear method may be better with the absolute error as limited condition. The adsorption process was spontaneous and endothermic.     

Generalized linear driving force approximation for adsorption of multicomponent mixtures

This work deals with the development of efficient numerical tools for the solution of diffusion dominated parabolic partial differential equations. This study finds its application in the modeling of the intraparticle mass balance necessary for describing dynamic adsorption processes.The orthogonal collocation method is proposed as the basis for developing generalized linear driving force approximations for adsorption and desorption of multicomponent mixtures in a single particle, independently of the mass transport model adopted. Based on this approach, it was possible to derive some approximations previously obtained from the analytical series of the homogeneous diffusion equation.Orthogonal collocation is also compared to other numerical methods found in the literature, using both the homogeneous diffusion and the dusty-gas mass transport models. The results show that orthogonal collocation is the more consistent approach.     

Predictive equations in gas adsorption kinetics

The experimental method of determining the operative parameters of adsorptive capacity and rate in the gas adsorption kinetics of packed bed sorbents relies upon the linear relationship between gas breakthrough time and sorbent weight. The slope and intercept of the straight line, resulting from such a plot, yields values for the gas saturation capacity and adsorption rate constant of the adsorbent. This relationship is shown in the modified Wheeler adsorption equation, originally derived from a continuity equation of mass balance between the gas entering an adsorbent bed and the sum of the gas adsorbed by plus that penetrating through the bed. We have found that for wellpacked adsorbent beds, the Dubinin-Polanyi equations for predicting adsorption space at equilibrium, based upon prior characterization of an adsorbent with a reference gas, could also be applied to gas flow conditions, and the kinetic capacity of the adsorbent predicted within close limits. Although no theoretical relationship exists for prediction of the adsorption rate constant, recent gas tests at high linear flow velocities have shown experimental evidence of the mass transfer limiting value for the rate constant. The functionalities of the kinetic saturation capacity and the mass transfer limited value for the adsorption rate constant have been incorporated into the modified Wheeler adsorption equation to provide an expanded equation permitting prediction by calculation of the breakthrough time of a gas through a well-packed bed of adsorbent granules.     

FITTING CASSAVA DRYING KINETIC WITH A HIGH ORDER EQUATION

The experimental drying curves with air flow rates of cassava parallelepipeds were analyzed at different and thickneses to obtain an empirical model for the cassava drying kinetics. Experimental results were modeled with first and higher order kinetic models. The kinetic parameters were fitted by non-linear regression to experimental drying curves with a power law model. The parameters of the power law model were statistically significant in a non-lineal joint interval confidence of 99%. The effect of temperature, air velocity and sample thickness on drying kinetic results, showed a consistent behavior with respect to drying theory.     

Adsorption of anionic textile dye Acid Green 9 from aqueous solution onto weak or strong base anion exchangers

The aim of this work is to study the thermodynamic and kinetic studies with regard to the adsorption of Acid Green 9 (AG9) on the most efficient resin, namely, acrylic weak base anion exchange resin with ethylenediamine‐functional groups (A1) selected from several anion exchange resins. The influence of the various experimental parameters such as, pH, initial dye concentration, contact time, temperature, and adsorbent dose was investigated by batch experiments. The extent of the dye adsorption increased with the decrease of the initial dye concentration and the increase of the contact time, temperature, and amount of the adsorbent. Adsorption process was quantitative and very fast at low concentrations of the dye. To investigate the mechanism of the adsorption and potential rate‐controlling steps, pseudo first‐ and second‐order, as well as intraparticle diffusion kinetic equations have been used. The adsorption kinetic of AG9 dye from aqueous solution onto A1 could be described by the pseudo second‐order reaction model. The obtained results are in agreement with the Langmuir and Freundlich models. In the optimum conditions established, an adsorption capacity of 500 mg textile dye (72% purity) g^?1 adsorbent (at 293 K) was reached. Desorption experiments by batch and dynamic methods were performed using a solution of 0.05 mol L^?1 NaOH. A series of 13 adsorption–desorption cycles were carried out by the dynamic method with a quantitative adsorption and the desorption efficiency higher than 95%. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009