Efficient Simulation of Chromatographic Processes Using the Conservation Element/Solution Element Method

Chromatographic separation processes need efficient simulation methods, especially for nonlinear adsorption isotherms such as the Langmuir isotherms which imply the formation of concentration shocks. The focus of this paper is on the space–time conservation element/solution element (CE/SE) method. This is an explicit method for the solution of systems of partial differential equations. Numerical stability of this method is guaranteed when the Courant–Friedrichs–Lewy condition is satisfied. To investigate the accuracy and efficiency of this method, it is compared with the classical cell model, which corresponds to a first-order finite volume discretization using a method of lines approach (MOL). The evaluation is done for different models, including the ideal equilibrium model and a mass transfer model for different adsorption isotherms—including linear and nonlinear Langmuir isotherms—and for different chromatographic processes from single-column operation to more sophisticated simulated moving bed (SMB) processes for the separation of binary and ternary mixtures. The results clearly show that CE/SE outperforms MOL in terms of computational times for all considered cases, ranging from 11-fold for the case with linear isotherm to 350-fold for the most complicated case with ternary center-cut eight-zone SMB with Langmuir isotherms, and it could be successfully applied for the optimization and control studies of such processes

Monitoring and robust adaptive control of fed-batch cultures of microorganisms exhibiting overflow metabolism [abstract]

Overflow metabolism characterizes cells strains that are likely to produce inhibiting by-products resulting from an excess of substrate feeding and a saturated respiratory capacity. The critical substrate level separating the two different metabolic pathways is generally not well defined. Monitoring of this kind of cultures, going from model identification to state estimation, is first discussed. Then, a review of control techniques which all aim at maximizing the cell productivity of fed-batch fermentations is presented. Two main adaptive control strategies, one using an estimation of the critical substrate level as set-point and another regulating the by-product concentration, are proposed. Finally, experimental investigations of an adaptive RST control scheme using the observer polynomial for the regulation of the ethanol concentration in Saccharomyces cerevisiae fed-batch cultures ranging from laboratory to industrial scales, are also presented

Parameter identification of the fermentative production of fructo-oligosaccharides by Aureobasidium pullulans

In this study, a mathematical model for the production of Fructo-oligosaccharides (FOS) by Aureobasidium pullulans is developed. This model contains a relatively large set of unknown parameters, and the identification problem is analyzed using simulation data, as well as experimental data. Batch experiments were not sufficiently informative to uniquely estimate all the unknown parameters, thus, additional experiments have to be achieved in fed-batch mode to supplement the missing information. © 2015 IEEE.funded by the Interuniversity Attraction Poles Programme initiated by the Belgian Science Policy Office. The authors thank the financial support from the F.R.S.-FNRS, the Belgium National Fund for the Scientific Research (Research Project 24643.08). C. Nobre thanks the Fundação para a Ciência e Tecnologia for the strategic funding of UID/BIO/04469/2013 uni

Sugars separation in a fermentative broth by simulated moving bed chromatography : SMB

Des sucres tels que les fructo-oligosaccharides (FOS) sont bénéfiques pour leurs hôtes car ils stimulent la croissance de bactéries bénéfiques dans le colon du fait qu’ils ne sont pas digérés par l’organisme. Ces FOS peuvent être produits à grande échelle par un procédé de fermentation du sucrose dont le milieu résultant (FOS + autres sucres + sels) doit être séparé en ses différents constituants afin de respecter les normes agroalimentaires. Parmi les techniques permettant cette séparation, seule la chromatographie liquide est applicable à grande échelle afin d’obtenir les puretés requises. La technique de séparation par lit mobile simulé (Simulated Moving Bed – SMB) permet de rendre le procédé continu et de diminuer la consommation d’éluant tout en augmentant la productivité. L’efficacité des techniques chromatographiques dépendant en grande partie de la nature de l’adsorbant, une étude préliminaire a été réalisée dans le but d’identifier le meilleur adsorbant pour cette séparation. Une résine échangeuse d’ions choisie, différentes techniques d’identification des paramètres de fonctionnement ont été mises en oeuvre afin de tester la séparation en mode SMB. Les résultats obtenus permettent de montrer qu’à partir d’un milieu de fermentation contenant 40% de FOS, il est possible d’obtenir un produit final pur à plus de 80%. Néanmoins, il a été mis en évidence que si la présence de sucrose dans le milieu de fermentation est inévitable, il faut absolument la contrôler au maximum pour éviter la pollution du produit finalFructooligosaccharides (FOS) are non-digestible sugars which affect positively the host by stimulating the growth of specific bacteria in the colon. At large scale, FOS can be produced from sucrose through fermentation. The fermentative broth obtained from this process is a complex mixture. The application of these sugars in the food industry requires their fractionation in order to meet final product specifications. Simulated moving bed chromatography (SMB) appears to be an efficient downstream process for the fractionation of sugars at an industrial scale. Thanks to this technique it is possible to work continuously reducing the solvent consumption and increasing the productivity. The major challenge when designing the separation process is the choice of an efficient adsorbent. A preliminary study was thus realized in order to identify the best adsorbent. An ion exchange resin was chosen and several parametric identification techniques were performed in order to realize the SMB separation. The results display the possibility to increase the FOS purity from 40% to 80%. Nevertheless, it was also displayed that sucrose present in the broth troubles the separation and must be strictly controlled during the fermentation

Sensitivity analysis and reduction of a dynamic model of a bioproduction of fructo-oligosaccharides

Starting from a relatively detailed model of a bioprocess producing fructo-oligosaccharides, a set of experimental data collected in batch and fed-batch experiments is exploited to estimate the unknown model parameters. The original model includes the growth of the fungus Aureobasidium pullulans which produces the enzymes responsible for the hydrolysis and transfructosylation reactions, and as such contains 25 kinetic parameters and 16 pseudo-stoichiometric coefficients, which are not uniquely identifiable with the data at hand. The aim of this study is, therefore, to show how sensitivity analysis and quantitative indicators based on the Fisher information matrix can be used to reduce the detailed model to a practically identifiable model. Parametric sensitivity analysis can indeed be used to progressively simplify the model to a representation involving 15 kinetic parameters and 8 pseudo-stoichiometric coefficients. The reduced model provides satisfactory prediction and can be convincingly cross validated.The authors thank the financial support from the F.R.S.-FNRS, the Belgium National Fund for the Scientific Research (Research Project 24643.08). C. Nobre thanks the Fundação para a Ciência e Tecnologia for the strategic funding of UID/BIO/04469 /2013 unit.info:eu-repo/semantics/publishedVersio

Systematic generation of identifiable macroscopic reaction schemes

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