C. B. Ching

An experimental study of a simulated counter-current adsorption system. I: Isothermal steady state operation

Abstract Results of an experimental study of a simulated counter-current adsorption system for separation of glucose-fructose mixtures are presented. Efficient separation may be achieved under a wide range of conditions. It is shown that the behaviour of the system, under steady state conditions, may be well described in terms of an equivalent counter-current flow system. Concentration profiles calculated from the dispersed plug flow model, with the dispersion coefficient calculated from pulse chromatographic measurements, provide a good representation of the experimental profiles. Alternatively the behaviour may be described in terms of the equilibrium stage model and the McCabe-Thiele diagram provides a useful means of visualizing the effects of changes in process conditions. The chromatographic HETP is about 10 cm and is approximately the same for both glucose and fructose and independent of fluid velocity, suggesting that axial mixing is more important than mass transfer resistance.

An experimental study of a simulated counter-current adsorption system—II. Transient response

Abstract The transient response of a simulated counter-current adsorption system has been studied experimentally. The experimental transient concentration profiles agree well with the theoretical profiles calculated from the equilibrium stage model with the number of theoretical stages estimated a priori from pulse chromatographic measurements.

Experimental study of a simulated counter-current adsorption system. IV: Non-isothermal operation

Abstract In an isothermal continuous counter-current adsorption separation process the product streams are generally diluted relative to the feed. However, this limitation does not apply to a non-isothermal system and it is shown that by applying a properly controlled temperature profile one may obtain the more strongly adsorbed species at a concentration substantially greater than the feed concentration. The practical feasibility of such a system is demonstrated experimentally for the separation of fructose-glucose mixtures. Under properly selected non-isothermal conditions an extract product containing 42% wt fructose (+2% glucose) was obtained from a feed mixture containing 24% of both fructose and glucose. The operation of the system and the proper choice of conditions can be understood by considering the McCabe-Thiele operating diagram.

Experimental study of a simulated counter-current adsorption system—VI. Non-linear systems

Abstract Operation of a simulated counter-current adsorption separation system has been studied experimentally and theoretically for a simple non-linear system (monoethanolamine-methanol separation on Duolite ion exchange resin). Non-linearity of the MEA isotherm imposes significant constraints on the allowable operating conditions. The behaviour of the system can be well predicted by a simple equilibrium stage model with concentration dependent distribution coefficients to account for non-linearity and coupling between the isotherms for the two components.

Dynamics of Simulated Moving-Bed Adsorption Separation Processes

Abstract Two mathematical models, namely the continuous moving-bed model (steady-state model) and the intermittent moving-bed model (transient model), have been used to describe simulated moving-bed adsorption separation processes. Four-column and 12-column simulated moving-bed systems for the separation of optical isomers with nonlinear adsorption isotherms were studied with the two models, respectively. The model equations were solved by using the numerical method of orthogonal collocation in finite elements. For the 4-column simulated moving bed, the differences between the simulation results from the two mathematical models are very obvious. Process dynamics, i.e., evolution of the species concentrations in the extract and raffinate and the axial profiles at different times, of the above systems in one switching period at the cyclic steady state are presented and discussed. They were numerically simulated with the intermittent moving bed model. The computations in a Cray J916 computer were very time c...

Kinetic and equilibrium study of the separation of three chiral center drug, nadolol, by HPLC on a novel perphenyl carbamoylated β-cyclodextrin bonded chiral stationary phase

A column packed with novel perphenyl carbamoylated β-cyclodextrin (β-CD) immobilized onto silica gel was used to separate nadolol by high performance liquid chromatography. Resolution of three of the four stereoisomers of nadolol was obtained by the complete separation of the most active enantiomer (RSR)-nadolol in reversed phase. The optimum separation condition for the mobile phase contained 80% buffer solution (1% TEAA, pH 5.5) and 20% methanol. The bed voidage, axial dispersion coefficient, overall mass transfer coefficients as well as equilibrium constants for the chromatographic enantiomeric separation were evaluated by moment analysis on the basis of solid film linear driving force model. The equilibrium constants were found to be 2.94, 3.46, and 5.45 for the (SRS)- and (SSR)-nadolol, (RRS)-nadolol, and (RSR)-nadolol, respectively. Their overall mass transfer coefficients were found to be 669.3, 846.3, and 106.4 min−1, respectively. The simulated results matched the experimental profiles quite well, which confirmed the validity of model parameters obtained in this study.

Experimental study of a simulated counter-current adsorption system—VII. Effects of non-linear and interacting isotherms

Abstract Continuous operation of a simulated counter-current adsorption process for separating a binary mixture with non-linear, interacting equilibrium relationships has been demonstrated experimentally. Emphasis is placed on the derivations of operating conditions for attaining high product purity and recovery when the isotherm is non-linear. With properly chosen flow conditions efficient separation is possible but the extract and raffinate products are generally recovered at concentrations lower than the feed. It is shown that this limitation can be avoided, and four our model system the extract product can be produced in high concentration and in relatively pure form by taking advantage of the effect of isotherm interaction. The suggested mode of operation may be applied, in principle, to increase the concentration of the extract product in any separation in which the adsorption equilibrium for the extract product components increases with increasing concentration of the raffinate product component. The practical feasibility of this mode of operation depends on the extend of the isotherm interaction.

Kinetic and equilibrium study of the enantioseparation of fluoxetine on a new β-cyclodextrin column by high performance liquid chromatography

SummaryA new β-cyclodextrin preparative chiral stationary phase was developed and utilized to separate racemic fluoxetine by high performance liquid chromatography. Kinetic and equilibrium constants for the chromatographic enantioseparation of racemic fluoxetine, using water and buffer (TTAA) as the mobile phase, were evaluated by moment analysis on the basis of equilibrium-dispersive and linear driving force models. Other parameters, including the voidage of the column and the axial dispersion coefficient, were also determined. The parameters obtained were used in the simulation of two single enantiomer band profiles. It was found that the experimental and simulated results match quite well confirming that the parameters used in simulation were correct.

Theoretical study of the effect of frit quality on chromatography using computational fluid dynamics

SummaryFrits at both ends of a chromatographic column, especially for a preparative column, have significant influence on the flow distribution within the column and thus the column efficiency. However, frits have received little attention from chromatographers in the past. Here a theoretical study was conducted with the aid of CFD software FLUENT to investigate the effect of frits on the performance of homogeneous and heterogeneous chromatographic columns. A dimensionless number,FQ, was applied to characterize frit quality. This study visualized how frit quality affects the flow distribution and the concentration band, the shape of eluted pulse at the colum exit and column efficiency. Simulation results show that the development length of the flow distribution is related toFQ but has nothing to do with the packing heterogeneity. The curvature of the concentration band in a column depends onFQ and packing quality. This study shows column efficiency can be improved significantly by increasingFQ and/or frit permeability.

Evaluation of Equilibrium and Kinetic Parameters of Smaller Molecular Size Amino Acids on KX Zeolite Crystals via Liquid Chromatographic Techniques

Abstract Liquid chromatographic techniques have been employed to evaluate the sorption and diffusion characteristics of smaller molecular size amino acids on large zeolite KX-type crystals. The three amino acids investigated in the present study were cysteine, threonine, and serine. All three amino acids adsorbed quite rapidly but there are significant differences in both the equilibrium constants and intracrystalline diffusivities. Combined with the kinetic and equilibrium data of the other three amino acids reported previously, it can be concluded that the larger molecules generally show a lower equilibrium constant. However, no obvious trend can be observed for intracrystalline diffusivity data.