The performance of molecular sieve adsorption columns: non-isothermal systems

A simple theoretical model is used to calculate dimensionless breakthrough curves and the corresponding temperature profiles for a non-isothermal adsorption column, operating under constant pattern conditions. The model involves three parameters α, which measures the relative rates of heat and mass transfer, β, which is a heat capacity term and λ, which measures the degree of non-linearity of the equilibrium isotherm. The effects of these parameters on the form of the concentration and temperature profiles is investigated. Experimental breakthrough curves for the non-isothermal sorption of propylene, cis-2-butene and 1-butene from an inert carrier gas, in a column packed with 5A molecular sieve, are analyzed and interpreted. The heat and mass transfer coefficients, calculated from the experimental curves, are shown to be consistent with independently measured values and conclusions are drawn concerning the nature of the controlling resistances.     

Comparison of experimental and predicted breakthrough curves for adiabatic adsorption in fixed bed

Mass and heat transfer in adiabatic fixed bed adsorbers is described by a model which considers resistance to mass and heat transfer simultaneously within the porous adsorbent particles and in the fluid flowing past the pellets. The adsorption equlibrium is described by a temperature dependent Freundlich isotherm.The mathematical model which is given in dimensionless form is solved numerically for different values of the dimensionless parameters.An example of predicted concentration and temperature breakthrough curves for an adiabatic integral bed is given. This prediction is performed solely on the basis of data from an isothermal differential bed. The predicted breakthrough time is within 8% of the experimental value when the dimensionless parameters are assumed constant and within 2% when their concentration and temperature dependence is taken into account.     

Theoretical and experimental SO2 adsorption onto pistachio-nut-shell activated carbon for a fixed-bed column

The adsorption and desorption behaviours of SO₂ onto activated carbons, which were prepared from pistachio-nut shells, were studied theoretically and experimentally in a fixed-bed column. A mathematical model considering non-equilibrium, non-isothermal and non-adiabatic effects for a single gas adsorbate on a fixed-bed system was derived and the model was solved by a finite-difference method. A linear driving force (LDF) approximation is used for heat and mass transfer rates. The temperature-dependent Langmuir equilibrium isotherm is used to represent gas–solid equilibrium isotherm. The theoretical study was conducted to compare the present model with the isothermal and adiabatic model. The effects of inlet concentration, flow rate and temperature were studied experimentally. These experimental data showed that the breakthrough time decreased with increasing feed concentration, increasing flow rate and increasing temperature and the trends were correctly predicted by the model calculations.     

Performance of the nonisothermal fixed bed adsorption column with nonlinear isotherms

The cell model approach for the analysis of nonisothermal fixed bed adsorption column has been presented under the assumption that adsorption is controlled by intraparticle diffusion and adsorption equilibrium is nonlinear. The numerical analysis has been carried out by the Runge-Kutta-Gill scheme. With the aid of a HITAC-8800 computer, the influence of controlling variables of the breakthrough curves and temperature curves has been made clear for such parameters as solid phase mass transfer coefficient, overall heat transfer coefficient at the column wall, length of bed and the equilibrium isotherms. A nonisothermal adsorption column can be designed adequately by applying the numerical method developed here according to the cell model approach.     

Thermal waves in an adsorption column: Parameter estimation

Adsorption experiments were carried out with a column packed with activated carbon particles, subject to a step input of carbon dioxide at the column inlet. From the measurements of a thermal wave advancing in the column the adsorption equilibrium constant, heat of adsorption and overall heat transfer coefficient were determined. Theoretical parameter sensitivity test also indicates that the adsorption equilibrium constant, heat of adsorption and overall heat transfer coefficient are the parameters of significance in this non-isothermal adsorption system. Discussion is also given on a heat generation and loss balance condition.     

SCALE ANALYSIS AND PARAMETRIC STUDY OF TRANSIENT HEAT/MASS TRANSFER IN THE PRESENCE OF NONPOROUS SOLID ADSORPTION

A transient, two-dimensional theoretical analysis of combined heat and mass transfer in the presence of adsorption/desorption is developed to study the fundamentals of heat and mass transfer dynamics. A parallel-plate rectangular channel is used as a model system. Appropriate surface boundary conditions for heat and mass transfer and adsorption/desorption interactions are formulated. A scale analysis of the governing equations is performed in order to identify the dimensionless physical parameters governing the process and to obtain the order-of-magnitude estimates for characteristic time constants of the system dynamics. Predictions of the scale analysis are validated against the results of the parametric study obtained through the numerical solutions of the governing equations. The findings demonstrate that the scale analysis is a very powerful analytical tool which allows one to evaluate the effects of different process parameters on heat and mass transfer dynamics in the presence of adsorption without performing the exhaustive numerical calculations.     

固定床动力学模型在离子交换过程中的应用

为了掌握所选的Thomas模型,Yoon-Nelson模型和Adams-Bohart模型在固定床米格列醇离子交换过程中的应用情况,实验借助对不同质量浓度的米格列醇溶液在定量树脂和固定流速下研究其在固定床中离子交换过程,并通过对透过曲线实验数据分析来验证相关固定床动力学模型在此过程中的有效性。结果表明:固定床上样液质量浓度增大,达到平衡饱和点的时间将缩短,传质区长度增大,吸附率变小,上样液质量浓度在8 mg/mL时吸附量达到最大;用动力学模型拟合透过曲线的过程参数,结果表明Thomas模型和Yoon-Nelson模型具有较好的相关系数,Thomas模型的速率常数和最大吸附量值随着上样液质量浓度的降低而增大,Yoon-Nelson模型的速率常数随着上样液质量浓度的降低而减小,且在Yoon-Nelson模型中计算得到的透过曲线中出口质量浓度与上样质量浓度比值为1/2时所对应的计算值和实验值相差很小,Thomas模型和Yoon-Nelson模型可用于该过程的离子交换性研究。     

色谱扰动-响应法测定C_8芳烃的吸附和传递参数

本文对固定床长吸附柱,在不考虑其轴向弥散时,简化了固定床恒温物料衡算方程,引入传递函数,导出测算吸附和传递参数的方法.此方法采用色谱-响应技术,在固定床吸附实验设备上,测定了C_3芳烃异构体各组分的吸附和传递参数,取得与工业操作相近似条件下,C_8芳烃的吸附相平衡常数和总传质系数.     

Theoretical prediction of temperature profiles in an adsorbent fixed-bed

The object of this paper is the theoretical study of the heat transfer in an adsorbent fixed-bed when the adsorption equilibrium is an irreversible one, the adsorption rate being limited by internal diffusion in particles. Then equations of the thermal wave put into a dimensionless form are proposed and discussed.It appears that the heat losses and the initial concentration of adsorbate in the fluid phase are important parameters for the heat transfer and that the thermal wave can grow before or behind the concentration front.     

Nonuniform channels in adsorbent monoliths

A model is introduced to account for nonuniform channel geometries in monolithic adsorbents. Based on nonisothermal operation, fully developed parabolic flow and the full three‐dimensional convection‐diffusion equation, the model is applied to the adsorption of dichloromethane from an air stream flowing through a binder‐less activated carbon monolith. The equilibrium parameters and the effective diffusion coefficient for adsorption are obtained independently from gravimetric adsorption experiments. The nonuniform channel model is capable of predicting breakthrough curves as a function of feed gas flow rates up to dimensionless breakthrough concentrations of about 0.4–0.6, depending on the feed flow rate. Even though the variation of effective diffusion coefficient with both concentration and temperature has been tested, successful prediction over the whole range of concentration may require the incorporation of further aspects relating to the anisotropic nature of the carbon. © 2010 American Institute of Chemical Engineers AIChE J, 2011     

活性炭纤维填充床内多组分竞争吸附

建立了活性炭纤维填充床内多组分竞争吸附传质动力学模型 ,采用正交配置方法求解数学模型以预测突破曲线 ,从理论上探讨了竞争吸附平衡及吸附质在填充床内的轴向弥散、纤维内扩散和纤维外对流传质等因素对强、弱吸附组分突破曲线的影响。在间歇和填充床吸附器内进行了脱除水溶液中酚类化合物的实验 ,测定了活性炭纤维吸附水溶液中苯酚和氯代苯酚的吸附等温线 (间歇吸附 )以及苯酚和氯代苯酚在活性炭纤维填充床内竞争吸附时的突破曲线 ,并与模型计算值进行了比较。结果表明 ,吸附质在活性炭纤维内扩散和纤维外对流传质阻力不是填充床内吸附过程的控制步骤 ,而轴向弥散影响显著 ,不可忽略     

MODELLING OF PROTEIN ADSORPTION IN A FIXED-BED: SINGLE AND TWO-SOLUTE BREAKTHROUGH BEHAVIOUR

Single- and two-solute adsorption breakthrough curves of lysozyme and bovine serum albumin on the cation exchanger SP-Sepharose Fast Flow were studied in this paper. A simplified mathematical model was used to model these data. Input parameters of the model such as equilibrium and kinetic parameters were estimated from single-solute batch experiments. For single-component adsorption in a fixed-bed, the breakthrough behaviour of lysozyme was well modelled. In contrast, significant deviations were observed between the measured and theoretical breakthrough curves of albumin. It was shown that the equilibrium parameters measured from batch experiments failed to account for the behaviour of albumin in the fixed-bed. The bisolute system consisting of the simultaneous adsorption of lysozyme and albumin was also modelled using the same set of parameters derived from single-solute batch experiments. Deviations were observed between the measured and theoretical breakthrough curves for both proteins, indicating that the effects of multicomponent equilibria and kinetics must be taken into consideration in parameter estimation.     

Sensitivity analysis of adsorption bed behavior: Examination of pulse inputs and layered-bed optimization

A mathematical model is developed to examine the sensitivity of the breakthrough of adsorption beds to system parameters. As the process model is integrated a single time, sensitivities are simultaneously calculated. The impact of mass and energy transfer effects and adsorbent layer thicknesses are determined by calculating the derivatives of the outlet concentration and outlet temperature. Several examples are considered. To establish a basis, the breakthrough of single beds is considered first. The adsorption of hexane on BPL activated carbon is contrasted with the adsorption of nitrogen on carbon molecular sieve, and combined mass and energy effects are considered by studying the adsorption of nitrogen on BPL activated carbon. The sensitivity data are then applied to determine the optimum bed layering of a two-layer, two-bed PSA system. The solution method presented can be adapted for the sensitivity analysis and subsequent optimization of a large number of adsorption systems.     

Equilibrium facilitated mass transfer in plate type reactive membrane separation devices

The introduction of mobile carrier species which react reversibly with the solute species in liquid membrane mass transfer separation devices can give enhanced mass transfer rate. For one-dimensional laminar boundary layer flow of a Newtonian fluid past a single-membrane separator with equilibrium facilitated transport inside the membrane, the mass transfer rate in the separator was analyzed numerically. For a Damköhler number equal to infinity, the effect of maximum facilitation factor, dimensionless equilibrium constant, dimensionless velocity and similarity transformation parameter on the performance of separators was investigated. The dependence of the membrane-fluid interfacial concentration and equilibrium facilitation factor on dimensionless velocity and similarity transformation parameter was discussed.     

蛋白质的膨胀床吸附过程穿透模型分析

引　言膨胀床吸附技术是近十几年来出现的一种新型生物分离模式 .该技术集细胞碎片清除、料液浓缩和蛋白质纯化等步骤于一身 ,大大提高了目标产物收率 ,降低了纯化时间和费用 .自 1993年Streamline系列膨胀床吸附介质和装置问世以来 ,国外已有不少利用膨胀床吸附技术提取蛋白质的报道[1,2 ] .已有研究表明 ,料液特性、吸附剂粒径等对膨胀床的流体力学特性和蛋白质在膨胀床内的吸附行为有着不同程度的影响[3～ 5] .考察这些影响因素有助于加深对膨胀床层析行为的理解 ,指导膨胀床层析的优化设计 .然而 ,由于膨胀床层析过程的复杂性 ,众多因素相互作用 ,某一参数的改变往往引起操作参数的系统性变化 ,因此实验条件下考察单一参数的改变对膨胀床层析过程的影响是不现实的[5,6 ] .　　　前期研究表明 ,对不同黏度的缓冲液 ,穿透模型能够较准确的预测蛋白质的穿透行为 .因此 ,本研究在前期研究的基础上[4 ,7] ,利用穿透模型分析了膨胀床吸附过程的质量传递和流体力学特1　穿透模型该模型假设[4 ,5] :①吸附剂颗粒为球形 ,有均一的尺寸和密度 ,离子交换基团均匀地分布在颗粒内部 ;②床内径向不存在浓度梯度 ;...     

Study of Adsorption Equilibrium and Dynamics of Benzene,Toluene, and Xylene on Zeolite NaY

The equilibrium and dynamics of low concentrations of benzene, toluene, and xylene in heptane adsorbed by zeolite NaY at 30, 40, and 50 °C were studied. The Langmuir equation was suggested to simulate the isotherms. Based on isotherms and material balances, multi‐component competitive adsorption isotherms can be successfully predicted by mono‐component adsorption isotherm parameters. A series of column adsorption experiments were conducted to study the adsorption dynamics. The mass transfer equations were solved by numerical analysis and used to describe the breakthrough curves, and the mass transfer coefficients in the adsorption column were obtained as well.     

Heat transfer to submerged surfaces in coarse-grained pressurized fluidized beds and fixed beds

This contribution reports on the theory underlying a uniform representation of heat transfer to submerged surfaces in fixed bed reactors and of gas convective part of heat transfer in fluidized beds with coarse-grained bulk solids and/or at elevated pressure. Based on an analysis of the pressure drop behaviour of fixed bed percolation at different gas pressures and with different bulk solids, a new dimensionless pressure drop parameter was developed. Fixed bed heat transfer data are very well correlated by this new dimensionless number. As soon as fluid throughput is in excess of minimum fluidization velocity, the pressure drop parameter transforms into the well-known Archimedes number. These two dimensionless numbers are connected by the condition of equilibrium for pressure drop and mass of practices in a fluidized bed. This equilibrium is fulfilled as soon as fluidization commences. Up to now, the Archimedes number has been generally accepted as the significant parameter, determining the gas convective part of heat transfer in fluidized beds; however, without any physical interpretation of this parameter. Introduction of the pressure drop number, which is consistent with the Archimedes number, reduces the heat transfer behaviour to pressure drop characteristics. The usefulness of this concept is proven by the comparison of experimental results and prediction.