RESUMEN

Today, monoliths are well-accepted chromatographic stationary phases due to several advantageous properties in comparison with conventional chromatographic supports. A number of different types of monoliths have already been described, among them recently a poly(high internal phase emulsion) (PolyHIPE) type of chromatographic monoliths. Due to their particular structure, we investigated the possibility of implementing different mathematical models to predict pressure drop on PolyHIPE monoliths. It was found that the experimental results of pressure drop on PolyHIPE monoliths can best be described by employing the representative unit cell (RUC) model, which was originally derived for the prediction of pressure drop on catalytic foams. Models intended for the description of particulate beds and silica monoliths were not as accurate. The results of this study indicate that the PolyHIPE structure under given experimental condition is, from a hydrodynamic point of view, to some extent similar to foam structures, though any extrapolation of these results may not provide useful predictions of pressure versus flow relations and further experiments are required.

Asunto(s)

Cromatografía/instrumentación , Cromatografía/métodos , Polímeros/química , Estirenos/química , Microscopía Electrónica de Rastreo , Modelos Teóricos , Tamaño de la Partícula , Presión

RESUMEN

Four optimization methods (Simplex, Rosenbrock, iterative factorial experimental design (IFED) and genetic algorithms) for the optimization of the biotechnological media composition under conditions where the measured quantities are subjected to the experimental error were compared. The computer simulations were performed on some of the selected two- to six- parameter biotechnological models. The optimization process was modified in such a way that the experimental error was considered. The results show that the optimization efficiency increases when this new termination criteria is implemented. In addition, the method efficiency becomes independent of the experimental error. In general, Simplex and Rosenbrock methods need fewer experiments and their distribution of necessary experiments is narrower than for IFED and genetic algorithms. The increase of model parameters that need to be optimized results in a decrease in the method efficiency and in an increase of the average number of required experiments. The results were further verified on the cultivation of Saccharomyces cerevisiae and were found to be in good agreement with the results obtained from the computer simulations.

RESUMEN

Monolithic supports have become the subject of extensive study in the past years. Despite their advantageous features and many successful chromatographic applications in the analytical scale, only a very few examples of larger volume monoliths were described. In the case of GMA-EDMA monoliths, this can be attributed to the fact that due to the exothermic polymerization a pronounced temperature increase inside the monolith significantly affects the structure. The temperature increase depends on the thickness of the monolith, and consequently, there is an upper limit that allows the preparation of a unit with a uniform structure. In the present work, we have analyzed a heat release during the polymerization and have derived a mathematical model for the prediction of the maximal thickness of the monolithic annulus having a uniform structure. On the basis of the calculations, two annuluses of different diameters were polymerized and merged into a single monolithic unit with a volume of 80 mL. In addition, a special housing was designed to provide a uniform flow distribution in the radial direction over the entire monolith bed. It was shown that such a monolithic column exhibits flow-independent separation efficiency and dynamic binding capacity up to flow rates higher than 100 mL/min. The separation and loading times are in the range of a few minutes. The pressure drop on the column is linearly dependent on the flow rate and does not exceed 2.5 MPa at a flow rate of 250 ml/min.

RESUMEN

We introduce the ratio of nonflocculent versus total biomass as a criterion for starting cell separation from the medium. This criterion can be applied for the automation of the process regardless of the process dynamics. Its minimum indicates the optimum period of time for the start of the separation process with regard not only to nonflocculent cell concentration, but also medium attributes. In contrast to the concentration of nonflocculent cells, which has two minima, first at the beginning of the process and another broader one in the period during which maximum flocculation is present, the ratio has a single minimum and can therefore be implemented as a criterion for cell separation. To calculate the ratio value, in addition to an on-line method for nonflocculent biomass measurement described elsewhere, an on-line method for the total biomass of flocculent yeast is proposed. It is based on the absorbency measurement of the cell biomass, previously deflocculated by EDTA. Therefore, it can be applied in bioprocesses with transparent media and yeast that can be deflocculated by EDTA. Copyright 1998 John Wiley & Sons, Inc.

RESUMEN

The ability of yeast to flocculate is important in different separation processes, especially in the beer industry. Because of the regulation purposes, there is a need for online monitoring. With the presented measuring set-up, consisting of a peristaltic pump, a photometer, and a computer, it is possible to determine the onset of flocculation as well as to follow flocculation intensity and the concentration of nonflocculated cells. It was found that for the yeast strain Saccharomyces cerevisiae ZIM 198 the decrease of nonflocculated cells (after flocculation has occurred) during the exponential growth can be described by an exponential equation for the first-order process, whereas the increase of free cells due to dispersion of the flocs during the stationary phase follows the form of the growth curve. It was also demonstrated that the absorbency profiles of yeast sedimentation can be described by the second-order equation suggested by Stradford and Keenan for the decrease of cell concentration during sedimentation. (c) 1997 John Wiley & Sons, Inc.