快速变压吸附制氧动态传质系数模拟分析

研究快速变压吸附制氧过程中的传质过程,结合实验数据对全局动态传质系数与常数传质系数进行对比模拟分析,并考察各传质阻力对传质效果的影响。结果表明：基于轴向、膜扩散和孔扩散估算的动态传质系数是有效的。膜阻力是主要阻力,其次是轴向扩散阻力,大孔扩散阻力较小,微孔扩散阻力可忽略。在快速变压吸附中,由于气速和温度变化较快,传质系数也会有较大变化,总体趋势是传质系数随着温度和气速的升高而升高。采用恒定传质系数无法准确描述吸附塔内各个时间点、空间点上的传质行为,根据各节点状态计算出的动态估算传质系数能够与吸附塔内的行为有较好的吻合度,模型具有较高的可信性。     

快速变压吸附制氧动态传质系数模拟分析

研究快速变压吸附制氧过程中的传质过程,结合实验数据对全局动态传质系数与常数传质系数进行对比模拟分析,并考察各传质阻力对传质效果的影响。结果表明:基于轴向、膜扩散和孔扩散估算的动态传质系数是有效的。膜阻力是主要阻力,其次是轴向扩散阻力,大孔扩散阻力较小,微孔扩散阻力可忽略。在快速变压吸附中,由于气速和温度变化较快,传质系数也会有较大变化,总体趋势是传质系数随着温度和气速的升高而升高。采用恒定传质系数无法准确描述吸附塔内各个时间点、空间点上的传质行为,根据各节点状态计算出的动态估算传质系数能够与吸附塔内的行为有较好的吻合度,模型具有较高的可信性。     

固定床吸附柱放大效应考察─—理论板当量高度分析

从色谱塔板理论公式出发，推导出实测理论板公式及理论极当量高度和吸附热力学、吸附动力学参数之间的关系，并对模型的选择、优化操作线速的选取作了讨论。实验测定了ｄ＿ｐ／ｄ＿ｔ＝４．０／２０．０时，吸附柱内的轴向扩散系数及流体传质系数，并加以关联。对不同压力、流量下的理论板当量高度也进行了检验。     

固定床吸附柱放大效应考察─—理论板当量高度分析

从色谱塔板理论公式出发，推导出实测理论板公式及理论极当量高度和吸附热力学、吸附动力学参数之间的关系，并对模型的选择、优化操作线速的选取作了讨论。实验测定了ｄ＿ｐ／ｄ＿ｔ＝４．０／２０．０时，吸附柱内的轴向扩散系数及流体传质系数，并加以关联。对不同压力、流量下的理论板当量高度也进行了检验。     

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。     

基于吸附-扩散机理研究钒离子透膜传质过程（Ⅱ）——钒离子透膜传质实验研究

吸附-扩散模型基于离子交换膜固定电荷理论,涉及离子选择性系数和透膜扩散通量,通过三种离子交换膜内VO2＋吸附平衡和透膜扩散实验,由吸附-扩散模型计算钒离子透膜扩散系数,揭示钒离子透膜传质过程。膜面FT-IR红外谱揭示基膜内不饱和键及RSO3-交换能力是影响膜稳定性和VO2＋膜内吸附量主要因素,膜面光滑、平整能有效地降低VO2＋吸附,抑制膜内水吸附和VO2＋透膜扩散。该模型能较真实揭示钒离子透膜传质过程,可快速有效的筛选电池隔膜,并指导高性能钒电池隔膜制备。     

活性炭吸附焦化纯苯中CS2的机理分析

对活性炭吸附焦化纯苯中CS2的吸附机理进行了初步探讨。用Freundlich方程关联出吸附等温线，并求出吸附热，结果表明吸附热较低，即吸附过程属典型的物理吸附。CS2在活性炭上的吸附动力学行为可用Elovich方程进行描述，传质系数在进料流速为1 mL／min时最大，与动态吸附试验结果一致。     

烷烃中少量芳烃的模拟移动床吸附及模拟

在实验研究烷烃中少量芳烃的模拟移动床吸附动态过程及其条件的基础上 ,用模拟移动床吸附模型进行了模型化拟合计算 ,传质采用线性推动力模型 ,得出轴向扩散系数和总传质系数。结果表明 :模拟移动床吸附动态模型的计算值与实验值相符 ;用吸附动态模型计算得出的轴向扩散系数与由关联式计算出的值相一致 ,且与流速成正比 ;总传质系数随着进料流量的增加而增大 ;区域 和区域 中 ,总传质系数随着温度和质量分数的升高而逐渐增大。区域 和区域 中 ,总传质系数随着温度的升高和质量分数的降低而逐渐减小。在低流量下 ,区域 和区域 中的总传质系数远比区域 和区域 中的总传质系数小。以上实验与计算结果为在直链烷基苯的生产过程中 ,降低循环烷烃中芳构化物的含量 ,实现延长脱氢催化剂的寿命提供了技术基础。     

丙酮在固定床上的吸附穿透曲线的数学模拟

固定床吸附过程是十分复杂的传质过程,本文在计算流体力学、计算传质学、计算传热学基础上,采用c'~2-ε_(c')双方程数学模型来模拟吸附过程,建立较严格的传质扩散模型。模型方程均采用有限体积法求解,并采用SIMPLEC算法求解耦合了压力和速度的动量方程。通过对比生产运行与模拟计算的穿透曲线,模拟结果与实验结果吻合良好,所建模型可用于生产运行中有关参数的预测。     

并流下行循环流化床反应器气固传质模型

建立了并流下行循环流化床反应器气固吸附传质模型,并采用稳态示踪的实验研究方法,测定了下行床中气相示踪剂浓度的轴向分布,进而利用Marquardt多元非线性回归方法求得了模型参数即轴向扩散系数和传质系数的值.实验结果的回归得到了模型参数与操作条件的经验关联式.该模型能很好的预计传质过程,包括轴向扩散系数和传质扩散系数的值以反应器中组分浓度的轴向分布,因此可用于描述并流下行循环流化床反应器的气固吸附传质过程.     

Dynamic modeling of fixed-bed adsorption of flue gas using a variable mass transfer model

This study introduces a dynamic mass transfer model for the fixed-bed adsorption of a flue gas. The derivation of the variable mass transfer coefficient is based on pore diffusion theory and it is a function of effective porosity, temperature, and pressure as well as the adsorbate composition. Adsorption experiments were done at four different pressures (1.8, 5, 10 and 20 bars) and three different temperatures (30, 50 and 70 °C) with zeolite 13X as the adsorbent. To explain the equilibrium adsorption capacity, the Langmuir-Freundlich isotherm model was adopted, and the parameters of the isotherm equation were fitted to the experimental data for a wide range of pressures and temperatures. Then, dynamic simulations were performed using the system equations for material and energy balance with the equilibrium adsorption isotherm data. The optimal mass transfer and heat transfer coefficients were determined after iterative calculations. As a result, the dynamic variable mass transfer model can estimate the adsorption rate for a wide range of concentrations and precisely simulate the fixed-bed adsorption process of a flue gas mixture of carbon dioxide and nitrogen.     

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.     

Numerical simulation of low-concentration CO2 adsorption on fixed bed using finite element analysis

Accurately predicting distributions of concentration and temperature field in fixed-bed column is essential for designing adsorption processes.In this study,a two-dimensional (2D),axisymmetric,nonisothermal,dynamic adsorption model was established by coupling equations of mass,momentum and energy balance,and solved by finite element analysis.The simulation breakthrough curves fit well with the low-concentration CO2 adsorp-tion experimental data,indicating the reliability of the established model.The distributions of concentration and temperature field in the column for CO2 adsorption and separation from CO2/N2 were obtained.The sensitivity analysis of the adsorption conditions shows that the operation parameters such as feed flow rate,feed concentra-tion,pellet size,and column height-to-diameter ratio produce a significant effect on the dynamic adsorption performance.The multi-physics coupled 2D axisymmetric model could provide a theoretical foundation and guidance for designing CO2 fixed-bed adsorption and separation processes,which could be extended to other mixed gases as well.     

多组分吸附过程的吸附速率模型

Three adsorption rate models are derived for multicomponent adsorption systems under either pore diffusion or surface diffusion control. The linear driving force (LDF) model is obtained by assuming a parabolic intraparticle concentration profile. Models I and Ⅱ are obtained from the parabolic concentration layer approximation. Examples are presented to demonstrate the usage and accuracy of these models. It is shown that Model I is suitable for batch adsorption calculations and Model Ⅱ provides a good approximation in fixed-bed adsorption processes while the LDF model should not be used in batch adsorption and may be considered acceptable in fixed-bed adsorption where the parameter Ti is relatively large.     

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.     

Development of design charts for fixed-bed adsorption

A mathematical model of the dynamic behaviour of non-isothermal fixed-bed adsorbers has been developed which takes into account the various mass and heat transfer resistances. Comparison of experimental and simulated results confirms that the model can predict the adsorption and desorption breakthrough curves of an adiabatically operated column, using only equilibrium data and tortuosity factors obtained from single pellet experiments. A simplified model with a reduced number of parameters was derived by investigation of the dimensionless transfer parameters under industrial conditions. It becomes evident that the main transfer mechanisms are convective heat and mass transfer in the bulk flow and diffusion within the pores of the particle. Dimensionless effluent concentration is expresses in terms of dimensionless time, a transport parameter, a non-isothermal parameter, the adsorption equilibrium and the inlet and initial concentrations and temperatures in the simplified model. For a chosen system of adsorbate and adsorbent, design charts can be developed by computer simulation, to determine graphically the breakthrough time as a function of significant process parameters, i.e. the dimensionless transfer parameter and the feed concentration.     

EXPERIMENTAL DETERMINATION AND PREDICTIONS OF BREAKTHROUGH CURVES IN A FIXED BED OF SILICA GEL USING THE TRANSFER UNIT APPROACH

A semi-empirical model was developed to predict the breakthrough curves of moisture adsorption on silica gel under different operating conditions. The model requires only the basic physical and transfer properties of the flowing gas stream. Experimental breakthrough curves were determined in this study for correlating some model parameters. These dynamic experiments were carried out with different values of the gas velocity, the inlet humidity, and the properties of the adsorbent. The breakthrough curves of the modified silica gel with neutron flux in a previous study were used to verify the proposed model. It is feasible to develop a single adsorption model to simulate the fixed-bed breakthrough curves for original and modified silica gels. The results show that the complex breakthrough curves can be predicted and are in very good agreement with the experimental data.     

EXPERIMENTAL DETERMINATION AND PREDICTIONS OF BREAKTHROUGH CURVES IN A FIXED BED OF SILICA GEL USING THE TRANSFER UNIT APPROACH

A semi-empirical model was developed to predict the breakthrough curves of moisture adsorption on silica gel under different operating conditions. The model requires only the basic physical and transfer properties of the flowing gas stream. Experimental breakthrough curves were determined in this study for correlating some model parameters. These dynamic experiments were carried out with different values of the gas velocity, the inlet humidity, and the properties of the adsorbent. The breakthrough curves of the modified silica gel with neutron flux in a previous study were used to verify the proposed model. It is feasible to develop a single adsorption model to simulate the fixed-bed breakthrough curves for original and modified silica gels. The results show that the complex breakthrough curves can be predicted and are in very good agreement with the experimental data.     

Study to investigate the importance of mass transfer of naproxen sodium onto activated carbon

In the present study, the adsorption of naproxen sodium onto activated carbons (BK4, obtained from white polymeric waste and SK4, obtained from black polymeric waste) was investigated by calculating the parameters of pH, contact time, the concentration of naproxen sodium and the temperature. The adsorption data of naproxen sodium onto activated carbon follows the Langmuir isotherm model and its kinetic processes were described by various kinetic adsorption models. It was determined that the pseudo-second-order model was the best choice among all the available kinetic models to describe the adsorption behaviour of naproxen sodium onto activated carbon. During the present study, the intraparticle diffusion rate constant, the external mass transfer coefficient and the film and pore diffusion coefficient were evaluated at various temperatures. In addition, the thermodynamic parameters of the adsorption of naproxen sodium onto activated carbon were also calculated.