Synergistic effects in competitive adsorption of carbohydrates on an ion-exchange resin

Model-based selection of the degree of cross-linking of cation exchanger resins for an optimised separation of monosaccharides

One of the main steps in designing preparative chromatographic separation units is the selection of a well-performing adsorbent. This is often based on expert knowledge or based on case studies of preselected adsorbents. Therefore, the selection is usually limited in terms of an optimised choice. In this contribution, a model-based optimisation of the selection of an adsorbent on the basis of correlations between structural adsorbent properties with model parameters of a transport dispersive model is proposed. Model parameters of glucose and xylose for five cation exchanger resins with varying degree of cross-linking are experimentally determined in a sequential approach. Void fractions and particle porosities were determined by pulse experiments with different tracers. Single-component isotherms were determined threefold via breakthrough curves with concentrations of up to 250 g l^-1 at 60 °C. Mass transfer coefficients were determined by batch experiments. Correlations between the degree of cross-linking of the resins and the Henry coefficients as well as the mass transfer coefficients were derived and applied in an optimisation case study. Based on the derived mathematical formula, the process performance of experimentally not investigated resins were predicted. Further, the selection of a resin for a preparative monosaccharide separation was included into optimisation algorithms.

Macroscopic and Microscopic View of Competitive and Cooperative Adsorption of Alcohol Mixtures on ZIF-8

While in most adsorptive separations different mixture components tend to compete for different adsorption sites, we report the existence of cooperative effects in the adsorption of alcohols (ethanol and 1-butanol) from the vapor phase on ZIF-8. The presence of these molecules in binary mixtures leads to an increase in their equilibrium capacities, compared to the pure component isotherms. These effects were first observed when predicting the mixture equilibrium capacities using the ideal adsorbed solution theory (IAST) and were also observed via grand canonical Monte Carlo (GC MC) simulations. GC MC simulations showed that the interaction between adsorbate molecules leads to the cooperative effect predicted by IAST. The predicted cooperative adsorption could be confirmed via breakthrough experiments. In these experiments, a "roll-up" of 1-butanol was observed during the regeneration of a ZIF-8 packed column. A dynamic breakthrough model employing IAST was developed and used to explain the effect of the adsorption equilibrium on the dynamic breakthrough profiles.

Modeling of type IV and V sigmoidal adsorption isotherms

Interpretation of type IV adsorption isotherms not by a composed but unified concept.

Competitive effect of glucose-fructose adsorption in a fixed-bed chromatographic column

A continuous separation system such as a simulated moving-bed process requires adsorption data with precise equilibrium and kinetic model parameters of a single chromatographic column. The adsorption of glucose and fructose in a fixed-bed chromatographic column was investigated to determine the competition effect of each component resulting from their initial molar ratios. The model parameters including bed porosity and axial dispersion coefficient were determined using the moment analysis method. The equilibrium isotherm parameters were estimated by conducting experiments at various molar ratios and initial sugar concentrations. The parameters obtained were then used for the simulation of dynamic breakthrough curves of glucose and fructose. The equilibrium isotherms revealed that the linear adsorption pattern provided good prediction for each molar ratio using the Henry equation. In addition, the modified Langmuir model was proposed to account for the competitive adsorption, due to the cooperative competition effect whereby glucose was promoted to the active sites by fructose to a greater degree than vice versa. A good agreement between the experimental and numerical data of the adsorption time profiles was also observed.

Glucose recovery from aqueous solutions by adsorption in metal-organic framework MIL-101: a molecular simulation study

A molecular simulation study is reported on glucose recovery from aqueous solutions by adsorption in metal-organic framework MIL-101. The F atom of MIL-101 is identified to be the most favorable adsorption site. Among three MIL-101-X (X = H, NH₂ or CH₃), the parent MIL-101 exhibits the highest adsorption capacity and recovery efficacy. Upon functionalization by -NH₂ or -CH₃ group, the steric hindrance in MIL-101 increases; consequently, the interactions between glucose and framework become less attractive, thus reducing the capacity and mobility of glucose. The presence of ionic liquid, 1-ethyl-3-methyl-imidazolium acetate, as an impurity reduces the strength of hydrogen-bonding between glucose and MIL-101, and leads to lower capacity and mobility. Upon adding anti-solvent (ethanol or acetone), a similar adverse effect is observed. The simulation study provides useful structural and dynamic properties of glucose in MIL-101, and it suggests that MIL-101 might be a potential candidate for glucose recovery.

Steady state recycling chromatography with an integrated solvent removal unit - separation of glucose and galactose

A process concept where a solvent removal unit is integrated to a steady-state recycling chromatography process (SSR-SR) offers a possibility to significantly increase the performance of single column chromatographic separation. The advantages of solvent removal for a difficult separation task at conditions typical for industrial scale chromatography were demonstrated by investigating the performance of SSR-SR in separation of glucose and galactose. Two limits for the extent of solvent removal were imposed: maximum total concentration of the solution fed into the column (viscosity limit) and the maximum total concentration achievable in the solvent removal unit (solubility or osmotic pressure limit). The process was optimized using numerical simulation. Three SSR-SR configurations with different positions of the solvent removal unit were compared with (1) the conventional batch process, (2) SSR without solvent removal, and (3) batch process with solvent removal. SSR-SR was found to always improve the productivity. In addition, solvent removal reduced eluent consumption in most cases. The concentration limits and the concentration of the fresh feed were shown to determine which SSR-SR configuration yields the best performance.

Pore-scale modeling of competitive adsorption in porous media

In this paper we present a smoothed particle hydrodynamics (SPH) pore-scale multicomponent reactive transport model with competitive adsorption. SPH is a Lagrangian, particle based modeling method which uses the particles as interpolation points to discretize and solve flow and transport equations. The theory and details of the SPH pore-scale model are presented along with a novel method for handling surface reactions, the continuum surface reaction (CSR) model. The numerical accuracy of the CSR model is validated with analytical and finite difference solutions, and the effects of spatial and temporal resolution on the accuracy of the model are also discussed. The pore-scale model is used to study competitive adsorption for different Damköhler and Peclet numbers in a binary system where a plume of species B is introduced into a system which initially contains species A. The pore-scale model results are compared with a Darcy-scale model to investigate the accuracy of a Darcy-scale reactive transport model for a wide range of Damköhler and Peclet numbers. The comparison shows that the Darcy model over estimates the mass fraction of aqueous and adsorbed species B and underestimates the mass fractions of species A. The Darcy-scale model also predicts faster transport of species A and B through the system than the pore-scale model. The overestimation of the advective velocity and the extent of reactions by the Darcy-scale model are due to incomplete pore-scale mixing. As the degree of the solute mixing decreases with increasing Peclet and Damköhler numbers, so does the accuracy of the Darcy-scale model.