Chromatographic adsorption with sinusoidal input

A chromatographic method based on a steady state sinusoidally varying input concentration has been developed and applied to the analysis of experimental data for some selected weakly adsorbing systems. Axial dispersion coefficients, zeolitic diffusivities and adsorption equilibrium constants determined by this method were shown to be consistent with the values derived by other methods of analysis. The proposed method is an improvement over pulse or step input chromatography in certain systems because simpler, less accurate measurements are required from experiments and the modelling process is mathematically less complicated.     

Rate Parameters in Heterogeneous Catalysis by Pulse Techniques

Response to perturbations of concentration and temperature have been used since the early part of the century [l, 21 to describe mathematically the transient behavior of process equipment. Beginning two decades ago [3, 41, evaluation of rate parameters, such as mass transfer coefficients, diffusivities, and chemical kinetic constants from response measurements, has developed into a useful tool in applied science. Kubin [5, 61 and Kucera [7] made a major contribution in pointing out that experimentally measurable moments of the response curves (peaks) to pulse inputs could be expressed explicitly in terms of the rate and equilibrium parameters used to describe the chemical and physical processes occurring in the equipment, For example, in a fixed-bed, continuously operating adsorber the moments of the response peak, in the effluent stream, to a pulse of concentration introduced in the feed could be expressed in terms of an axial dispersion rate coefficient, fluid-to-particle mass transfer coefficient, intraparticle diffusivity, and adsorption rate and equilibrium constants at an interior site in the adsorbent particles.     

Rate Parameters in Heterogeneous Catalysis by Pulse Techniques

Response to perturbations of concentration and temperature have been used since the early part of the century [l, 21 to describe mathematically the transient behavior of process equipment. Beginning two decades ago [3, 41, evaluation of rate parameters, such as mass transfer coefficients, diffusivities, and chemical kinetic constants from response measurements, has developed into a useful tool in applied science. Kubin [5, 61 and Kucera [7] made a major contribution in pointing out that experimentally measurable moments of the response curves (peaks) to pulse inputs could be expressed explicitly in terms of the rate and equilibrium parameters used to describe the chemical and physical processes occurring in the equipment, For example, in a fixed-bed, continuously operating adsorber the moments of the response peak, in the effluent stream, to a pulse of concentration introduced in the feed could be expressed in terms of an axial dispersion rate coefficient, fluid-to-particle mass transfer coefficient, intraparticle diffusivity, and adsorption rate and equilibrium constants at an interior site in the adsorbent particles.     

大型液相色谱分离过程参数辨识新方法

本文提出大型液相色谱分离过程流体轴向扩散系数、吸附相平衡常数和总传质系数参数辨识模型,用惰性物为示踪剂扰动应答实验技术和色谱测量技术测定参数。结果表明:在轴向扩散中,涡流扩散占主导地位;轴向扩散系数随流体流速以及装填密度的增大而增大;相平衡常数比总传质系数有较高灵敏度;葡萄糖果糖的相平衡常数随温度的升高而降低,而总传质系数随流体流速和温度的增大而增大;得到理论流出曲线与实验流出曲线一致的结果。     

SMB chromatography design using profile advancement factors,miniplant data,and rate‐based process simulation

This article describes a systematic miniplant‐based approach to rapid development of simulated moving bed (SMB) chromatography applications. The methodology involves analysis of single‐column pulse tests to screen adsorbents and operating conditions and to determine initial values of profile advancement factors used to specify flow rates for an initial SMB miniplant experiment. A lumped‐parameter linear driving force rate‐based model is developed by fitting process data from a single miniplant run. The data are fit in a two‐step procedure involving initial determination of effective adsorption isotherm constants as best‐fit parameters with subsequent adjustment of calculated mass transfer coefficients to refine the data fit. The resulting simulation is used to guide further miniplant work and minimize experimental effort. The methodology is illustrated with miniplant data for a binary protein separation showing excellent agreement between model results and process data generated over a wide range of operating conditions. © 2009 American Institute of Chemical Engineers AIChE J, 2009     

脉冲-应答技术测定传递与吸附系数和动力学系数

本文运用脉冲-应答技术,在不同温度和不同流速条件下测定了糠醛在BHK-1催化剂上的传递与吸附系数和加氢反应速率常数.依据修正过的Kubin-Kucera气-固相传质-维扩散模型,采用比较准确的Fourier分析法处理实验结果,并通过最优化计算求得了E、D_e、K_f、k_a、K_a、K_r,等6个参数.     

Determination of lumped rate coefficients of proteins: Effect of adsorption

The equilibria and kinetics of adsorption of lysozyme and bovine serum albumin on the Fractogel-EMD tentacle-type cation exchanger and the Fractogel-TSK conventional cation exchanger have been studied experimentally by batch stirred-tank method. Adsorption equilibrium data corresponded well to the Langmuir isotherm. For both proteins, the tentacle-type exchanger exhibited a higher binding capacity than the conventional exchanger. This is attributed to the flexibility of the functional groups in the tentacle-type exchanger which enhance optimal electrostatic interactions. The dynamic data were analyzed by a simplified data model which lumped mass transfer resistances and intrinsic adsorption kinetics into a single rate constant. For both proteins, it was found that the tentacle-type exchanger showed a smaller lumped rate coefficient than the conventional exchanger. The difference in the values of the lumped rate coefficients was shown to be due to the influence of nonlinear equilibrium constants rather than due to any difference in rate of adsorption.     

EPA和DHA在超临界流体色谱柱中的传质动力学

用超临界流体色谱 (SFC)法研究了EPA和DHA在C18上的吸附和传质性能 .建立了色谱动力学模型并获得了模型参数 ,较好地拟合了实验流出曲线 .结果表明吸附平衡、轴向弥散、流体相传质和颗粒内有效扩散都是影响SFC分离EPA和DHA的重要因素     

Adsorption separation of N2, O2, CO2 and CH4 gases by β-zeolite

In the present study, adsorption equilibrium and kinetic separation potential of β-zeolite is investigated for N₂, O₂, CO₂ and CH₄ gases by using concentration pulse chromatography. Adsorption equilibrium and kinetic parameters have been studied. Henry’s Law constants, heat of adsorption values, micro-pore diffusion coefficients and adsorption activation energies are determined experimentally. The three different mass transfer mechanisms, that have to take place for adsorption to occur, are discussed. From the equilibrium and kinetic data, the equilibrium and kinetic selectivities are determined for the separation of the gases studied.With β-zeolite, carbon dioxide has the highest adsorption Henry’s Law constant at all the temperatures studied, followed by methane, nitrogen and oxygen. Carbon dioxide separation from oxygen, nitrogen and methane has good equilibrium separation factors. This factor is not very high for methane/nitrogen and methane/oxygen systems and is the lowest for nitrogen/oxygen system. Micro-pore diffusion is the dominant mass transfer mechanism for all the systems studied, except CH₄, with β-zeolite. The kinetic separation factors are very small at high temperatures for all the systems studied. Nitrogen/carbon dioxide and oxygen/carbon dioxide can be separated in kinetic processes with reasonable separation factors at low temperatures. Both equilibrium and kinetic separation factors decrease as column temperature increases. Considering all the observations from this study, it was concluded that β-zeolite is a good candidate for applications in flue gas separations, as well as natural gas and landfill gas purifications.     

Pulse Chromatographic Studies of Adsorption of CO2, CH4, and N2 Using Amine Functionalized Polystyrene Adsorbents

Adsorption of CO₂, CH₄, and N₂ was investigated using pulse concentration chromatography on polystyrene functionalized by covalently attached diethanolamine, dimethylamine, imidazole, and N-methyl piperazine. The adsorption equilibrium constants at different temperatures were estimated by fitting the experimental chromatograms into a non-linear equilibrium dispersive chromatography model using gPROMS. Axial dispersion was found to be the controlling mechanism for dispersion of the chromatograms. The heat of adsorption and corresponding equilibrium selectivities were determined from the adsorption equilibrium constants. The imidazole based adsorbent showed the highest affinity for CO₂.     

Dynamics of three-phase slurry reactors

The dynamic behavior of three-phase slurry systems is presented in terms of the response characteristics of the reactor to a pulse or step input. Equations are derived for the steady-state conversion and the first moment of the response in the gas phase to pulse input of concentration. Overall irreversible and reversible first-order reactions, and adsorption-reaction processes at the catalyst surface have been considered from the viewpoint of evaluating rate coefficients from measured response data. Analysis of two-step adsorption-reaction processes is particularly interesting since dynamic data offer the possibility of separate evaluation of adsorption and surface reaction rate constants, which is not possible from steady-state measurements.     

Measurements of particle-to-gas mass transfer coefficients from chromatographic adsorption experiments

From chromatographic adsorption experiments, adsorption equilibrium constants and particle-to-gas mass transfer coefficients were determined by fitting tracer output signals in the time domain. The results indicate that the Sherwood numbers are far less than the limit of two for a single particle.     

Transient operation of a catalytic liquid-liquid plug flow reactor for kinetics measurements

A centrifugal partition chromatograph (CPC) was used as a liquid-liquid catalytic reactor for the isomerisation of hexen-3-ol into ethylpropylketone with a water soluble rhodium catalyst. Global mass transfer coefficients were measured and shown to depend on both the nature of the solute and the flow rate. Liquid-liquid partition isotherms were also determined with the CPC using elution chromatography. Finally, a reactor model was derived to account for the experimental results obtained both under stationary and transient (pulse) conditions. A parameter sensitivity evaluation is also presented.     

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.     

Rate parameters from dynamic experiments with single catalyst pellets

Equations have been derived relating the rate and equilibrium parameters for adsorption and reaction on a single catalyst pellet to measurable properties of pulse-response experiments. In particular, it is shown that intraparticle diffusivities, adsorption equilibrium constants, and adsorption rate constants can be evaluated from the moments of the response peak from one end face of a catalyst pellet when a pulse of diffusing component is passed over the other end face.The method is illustrated with experimental data for helium (in nitrogen) and cyclopropane (in helium) pulses diffusing through alumina pellets at 35–90°C and atmospheric pressure.The results suggest that this dynamic procedure offers a rapid, simple method for establishing the rate and equilibrium parameters for adsorbing systems, provided all processes are linear. An advantage is that the intraparticle diffusivity can be obtained from the first moment of the response peaks, without recourse to the less accurate, second moment. Extension of the method to first-order reaction systems is discussed. A disadvantage is that the results may not be of high accuracy when many parameters are to be evaluated from one set of data; i.e. from one set of experimental conditions.     

Nickel-catalyzed hydrogenation of soybean oil: I. Kinetic,equilibrium and mass transfer determinations

The kinetic and equilibrium constants were determined for the hydrogenation of soybean oil on a commercial nickel catalyst in a 300-ml Parr batch reactor. These constants were used to calculate the hydrogen gas absorption coefficients by coupling mass transfer with reaction rate based on a Langmuir Hinshelwood model. The activation energy for the rate-determining step was 23 kcal/g mol whereas the adsorption energy for hydrogen was −12.5 kcal/g mol. The gas absorption coefficients varied between 0.3 to 0.7 min⁻¹ as the temperature ranged between 140–180 C.     

Interpretation of chromatographic peaks by fourier analysis

Extraction of model parameters, such as kinetic rate coefficients, equilibrium constants and transport rate coefficients, may be obtained by determining the coefficients of the Fourier series which describe chromatographic peaks. Error buildup due to noise occurs slowly with successive harmonics in contrast to the rapid buildup in successive moments which make higher moments unreliable for extracting model parameters. Fourier analysis is applied to the simplest case of axial dispersion in a non-porous, non-adsorbing packing and to the important case of adsorption on a porous packing. Expressions for the Fourier coefficients, amplitude ratios and phase lags are derived for the axial dispersion case, the Kubin-Kucera model for adsorption on a porous packing and, as well, for the case of axial dispersion and inter-particle diffusion without adsorption.     

A new approach to evaluate kinetic parameters and mass transfer coefficients in continuous stirred tank reactors. Application to antibiotic separation

A new method is proposed to evaluate kinetic parameters and mass transfer coefficients for adsorption processes carried out in continuous stirred tank reactors. This method, employing a biphasic model, does not linearize nonlinear solute concentration versus time data, nor does it assume the existence of equilibrium in a typical nonequilibrium situation as is currently done. For a nonlinear adsorption isotherm, the coupled differential equations need to be solved numerically, but using an elegant analytical solution it is possible to determine rate constants and mass transfer coefficients in the case of nonlinear kinetics with a linear adsorption isotherm. This solution (biphasic model, linear isotherm) is obtained and compared with solutions incorporating (i) a linear model (linear isotherm) and (ii) a numerical solution (nonlinear isotherm) for recovery of the antibiotic novobicoin in stirred tank reactors. For novobiocin adsorption versus time data, use of the biphasic model results in a lower mean percentage error than either the linear model or the numerical simulation; further, it provides a far superior fit of short-time adsorption behavior. Hence, we strongly advocate that the biphasic model be routinely employed along with linear models and numerical simulations of Langmuir/Freundlich isotherms for interpretation of adsorption data.     

Reliability and limitations of pulse chromatography in evaluating properties of flow systems: 1. modelling and experimental considerations

Reproducibility of response characteristics and parameters derived therefrom, and adequacy of the Kubin-Kucera model for pulse chromatography were investigated experimentally using the physisorption of methane and ethane on silica gel. Reproducibility was found to be excellent, while the agreement of predicted and observed effects of velocity, particle size, temperature and bed length on model parameters confirmed the adequacy of the model. Agreement of the pore diffusivity and the adsorption equilibrium constant with values measured by other techniques provide further support for the model. Rearrangement of model terms shows that the rate coefficient for physisorption and the mass transfer coefficient cannot be measured using chromatography.     

Rate constants of elementary steps by pulse technique

Two methods for measuring the rate constants of the elementary steps by the pulse technique are proposed. The first gives the adsorption and the desorption rate constants from the retention time and the half width of the chromatographic peak, and was applied to the adsorption of benzene on HY and CaY zeolites. The second gives the surface reaction rate constant and the desorption rate constant of the reactant from the peak of the product which is not adsorbed on the catalyst surface. The method was applied to the cracking of cumene on HY and CaY.