Ernst Jan de Place Hansen

Mass transfer properties of monoliths

The mass transfer properties of polyglycidylmethacrylate–ethylenedimethacrylate monolithic ion-exchangers (convective interaction media disks) were evaluated. As a reference material, the particulate ion-exchanger Source 30 was selected. The model proteins lysozyme, bovine serum albumin, and IgG were loaded at different concentrations and velocities. The mass transfer zones obtained with the monoliths were affected by neither the linear flow velocity nor the protein concentration in the mobile phase. The reduced height equivalent to one theoretical plate (HETP) of monoliths were independent of the reduced velocity. This was not the case for the particulate material.

Whey proteins as a model system for chromatographic separation of proteins

Although chromatographic separation of whey proteins has been considered too expensive, whey may serve as an excellent model mixture to investigate and validate the use of simulation tools in the development and optimization of chromatographic separations and the outcome could easily be utilized since the model system has an intrinsic value. Besides, milk from transgenic animals could be an attractive source of pharmaceuticals which must be separated from the other proteins in the milk. Several whey proteins are of interest especially, alpha-lactalbumin, beta-lactoglobulins, immunoglobulins, lactoperoxidase, and lactoferrin. The scope of the project is to develop a consistent set of chromatographic data for whey proteins including isotherms, transport properties and scale-up studies and to develop the appropriate models for the anion exchangers Q-Sepharose XL, Source 30Q, Ceramic Q-HyperD F, and Merck Fractogel EMD TMAE 650 (S). In this work we have determined and correlated gradient and isocratic retention volumes in the linear range of the isotherm for alpha-lactalbumin, beta-lactoglobulin A and B, and bovine serum albumin at a pH from 6 to 9 at various NaCl concentrations.

Application of the two-film theory to the determination of mass transfer coefficients for bovine serum albumin on anion-exchange columns.

The paper describes a method of simultaneous determination of the external and the solid-phase mass-transfer coefficients from frontal analysis data. The protein flux to the solid particles is determined from the slope of the breakthrough curve and the mass-transfer coefficients are determined by fitting the two-film model to the experimentally determined flux. The two-film model is compared with two apparent overall driving force models: the apparent overall mobile phase driving force model and the apparent overall solid-phase driving force model. The experiments show that the apparent overall driving force models fail to describe the flux correctly and this is substantiated by the theory. Results obtained with bovine serum albumin on the anion-exchange media Q HyperD, Source, and Poros show that the external film resistance is significant for Reynolds numbers less than one. The experimental Sherwood numbers are lower than expected and their dependence on the Reynolds number are much higher than expected.

Overall mass-transfer coefficients in non-linear chromatography

In the case of mass transfer where concentration differences in both phases must be taken into account, one may define an overall mass-transfer coefficient based on the apparent overall concentration difference. If the equilibrium relationship is linear, i.e., in cases where a Henrys law relationship can be applied, the overall mass-transfer coefficient will be concentration independent. However, in mass-transfer operations, a linear equilibrium relationship is in most cases not a valid approximation wherefore the overall mass-transfer coefficient becomes strongly concentration dependent as shown in this paper. In this case one has to discard the use of overall mass-transfer coefficients and calculate the rate of mass transfer from the two-film theory using the appropriate non-linear relationship to calculate the equilibrium ratio at the interface between the two films.

The Influence of Retention on the Plate Height in Ion-Exchange Chromatography

Abstract The plate heights for the amino acid tyrosine (anion exchange) and the polypeptide aprotinin (cation exchange) were determined on a porous media (Resource 15) and a gel filled media (HyperD 20) at salt concentrations ranging from weak to strong retention. At a constant velocity, measurements showed that the plate height increase with increasing retention, went through a maximum, and finally, decreased as the retention increased, i.e., when the salt concentration was lowered further. The band broadening of a chromatographic peak in the column was caused by the axial dispersion and mass transfer. In this article, the rate of mass transfer in the particles is described by three different rate mechanisms, pore diffusion, solid diffusion, and parallel diffusion. The van Deemter equation was used to model the data to determine the mass‐transfer properties. The development of the plate height with increasing retention revealed a characteristic behavior for each rate mechanism. In the pore diffusion model, the plate height increased toward a constant value at strong retention, while the plate height in the solid diffusion model decreased, approaching a constant value at strong retention. In the parallel diffusion model, both pore and solid diffusion took place. Therefore, the parallel diffusion model coincides with the pore diffusion model at weak retention and with the solid diffusion model at strong retention, while a maximum is reached at intermediate retention, resulting in a bell‐shaped curve. This behavior corresponds to the observed variation of the plate height at constant velocity. Neither the pore nor the solid diffusion model can describe the experimental data while a satisfactory fit was obtained using the parallel diffusion model.

Employment and winter construction: a comparative analysis of Denmark and western European countries with a similar climate

Reduced seasonal building activity in the construction sector is often assumed to be related to hard winter conditions for building activities and poor working conditions for construction workers, resulting in higher costs and poor quality of building products, particularly in the northern hemisphere. Can climatic conditions alone explain the sizeable difference in reduction in building activity in the construction sector in European countries in the winter months, or are other factors such as technology, economic cycles and schemes for financial compensation influential as well? What possibilities exist for reducing seasonal variation in employment? In addition to a literature review related to winter construction, European and national employment and meteorological data were studied. Finally, ministerial acts, ministerial orders or other public policy documents related to winter construction were scrutinized in order to identify and compare economic incentives and compensation schemes intended to increase winter working in construction in Denmark and other western European countries. Overall, economic development in the construction sector and the level of compensation or the duration of contracts for workers is more likely to explain differences in seasonal activity than climatic or technological factors.