C. Nobre acknowledges the F.C.T. - Fundacao para a Ciencia e a Tecnologia (Portugal) for the PhD Grant ref. SFRH/BD/32514/2006. A. Severino is funded by Belgian Fund for Scientific Research (F.S.R.- FNRS).This paper presents research results of the Belgian Network DYSCO (Dynamical Systems, Control, and Optimization), funded by the Interuniversity Attraction Poles Programme, initiated by the Belgian Federal Science Policy Office (BELSPO). The scientific responsibility rests with its authors

De Weireld, Guy

Nobre, C.

Retamal, Cristina

Rodrigues, L. R.

Severino, Antoni

Teixeira, J. A.

Wouwer, Alain Van de

Nobre, Clarisse

Universidade do Minho: RepositoriUM

OPERATING CONDITIONS OF A SIMULATED MOVING BED CHROMATOGRAPHY UNIT FOR THE PURIFICATION OF FRUCTO-OLIGOSACCHARIDES  Clarisse Nobre José António Teixeira Lígia Rodrigues IBB – Institute for Biotechnology and Bioengineering, Centre of Biological Engineering University of Minho Campus de Gualtar 4710–057 Braga Portugal E-mail: clarissenobre@deb.uminho.pt    Antoni Severino2 Cristina Retamal1 Guy De Weireld2 Alain Van de Wouwer1  University of Mons 1Control Department 2Thermodynamic Department Boulevard Dolez 31  7000 Mons Belgium    KEYWORDS FOS, Fermentative broth, PS-DVB resins, SMB   INTRODUCTION  In recent times, the production of fructo-oligosaccharides (FOS) has gained large commercial interest due to its beneficial properties in the human health through modulation of the microbiota. Based on these benefits, FOS, such as kestose (GF2), nystose (GF3) and fructo-furanosilnystose (GF4), have been denominated as prebiotics (Gibson, 1998).  In large scale, FOS can be produced by fermentation of sucrose through fructosyltransferase that is present in several microorganisms. Fermentative processes have high production yields compared with other processes. However, the composition of the final broth from a fermentative process includes not only FOS, but also di and mono-saccharides, namely sucrose (S), fructose (F) and glucose (G) that do not contribute to the beneficial properties as prebiotics and must be removed from the oligosaccharides mixture.  Among other separation processes, simulated moving bed (SMB) chromatography appears to be an efficient downstream process for the fractionation of sugars in an industrial scale, since it is a continuous process and high productivities can be obtained with low consumption of reagents (Gomes et al., 2006); see Figure 1.  The first step to study the separation of compounds by SMB is the choice of an efficient adsorbent. Ion exchange resins of sulfonated poly(styrene-co-divinylbenzene) (PS-DVB) have been largely used as adsorbent in the sugar industry due to their chemical inertness, higher capacity and selectivity (Luz et al., 2008, Tiihonen et al., 2002). These non-ionic resins can be functionalized with cations such as potassium. Potassium cations form weak complexes with sugars providing high kinetic adsorption rates (Pedruzzi et al., 2008). The separation using these resins occurs due to both size exclusion and restricted diffusion effects (Nobre et al., 2009).  IIIIIIIVDesorbent D Extract EFeed FRaffinate RsolidliquidABABS + A S + A + BS + BSD D + BD + A D + A + BD + BD + A + BD + ADBA Figure 1. Equivalent counter-current representation of a simulated moving bed process – Material flows and adsorption-desorption phenomena in each section  METHODS AND MATERIALS  In this work, two gel-type PS-DVB resins in the potassium form were studied namely, Dowex 50W-X2 (particle size: 37-74 µm) and Dowex Monosphere 99K/320 (particle size: 320 µm). Experiments were carried out in a batch column (1.6x30 cm) in order to determine adsorption parameters.  Salts present in the fermentative broth are mainly sodium (65%) and potassium (34%). Potassium resins were used so that sodium ions could replace potassium in the resin affecting its adsorption characteristics. To guarantee a minimum of 90% of potassium in respect to sodium ions in the final solution the broth was pre-treated. After removing the biomass by filtration (0.2 µm), 250 mL of broth, in batch steps, were saturated with potassium ions by passing the broth through a column with 100 mL of Dowex Monosphere 99K/320. Before starting another batch, the column was washed with ultra-pure water and regenerated with K2SO4 solution (0.5 mol/dm3)   RESULTS AND DISCUSSION  In order to verify the separation performance, pulse tests of each sugar were performed in a batch column connected to an HPLC system equipped with an RI detector. Sugars were found to be adsorbed by both resins in the following order: F>G>S>GF2>GF3>GF4. Moreover, with Dowex 50W- X2 it was possible to separate salts from sugars. However, the chromatograms obtained for Dowex Monosphere 99K/320 showed broader peaks for G, F and GF due to a slower kinetics caused by large particles.  Sugars adsorption showed linear equilibrium for the range of concentrations used. Thus, using the retention time method described in Guiochon et al., 1994, it was possible to determine the Henry constants for the two groups present in the broth: FOS and SGF (sucrose+glucose+fructose).   Assays conducted with high flow-rates of eluent (above 20 mL/min) showed high compressibility of the particles for Dowex 50W-X2, causing a back pressure in the column up to the maximum allowed by the SMB system (60 bars). On the other hand, Dowex Monosphere 99K/320 appeared to be stable at high flow-rates keeping a constant porosity. Therefore, Dowex Monosphere 99K/320 was found to be suitable to work in the SMB unit.  A mathematical model was used to predict the elution profile and validated with experimental results. This model consists of 4 mass balance partial differential equations, 2 for the concentrations in the liquid phase and 2 for the concentrations in the solid phase:  ( )i i ieqiF,i i ic q c1t t zq k q qt∂ ∂ ∂− ε+ = −ν∂ ε ∂ ∂∂= −∂  where ci and qi are the concentration of the component i in the liquid and solid phase respectively, t is the time, ε is the porosity, z is the axial coordinate, v is the fluid velocity  and kF,i is the mass transfer coefficient.  A LDF model (Ruthven, 1984) is used for mass transfer kinetics. The equilibrium concentration is given by a linear isotherm where H is the Henry coefficient.   eqi i iq H c=   These model PDEs are solved in Matlab with the toolbox MatMol (www.matmol.org; (Wouwer et al., 2004) using a method of lines approach, i.e. spatial discretization followed by time integration of the resulting semi-discrete (discrete in space but continuous in time) equations. As the concentration profiles develop steep moving fronts, the application of finite difference schemes lead to spurious oscillations in the concentration profiles, as illustrated in Figure 1, even when using upwind schemes for the convective terms and a relatively large number of spatial grid points.     Figure 2: Time evolution of the spatial concentration profiles inside a chromatographic column, computed with finite differences with a 4-point biased upwind scheme, and N = 400 grid points.   To alleviate this problem, nonoscillatory schemes can be used such as Koren slope limiters, as illustrated in Figure 2.     Figure 3: Time evolution of the spatial concentration profiles inside a chromatographic column, computed with a Koren slope limiter scheme, and N = 100 grid points   The use of this scheme is quite efficient and leads to the following time evolution at the column outlet. The numerical simulation results are also compared with experimental data, showing a relatively good fit using the model parameters determined in the batch experiments. 0 0.05 0.1 0.15 0.2 0.25-101234567zConcentration (g/L)Profile inside the column  C FOSC SGF0 0.05 0.1 0.15 0.2 0.25-0.500.511.52zConcentration (g/L)Profile inside the column  C FOSC SGF  Figure 4: Time evolution of the (RI signal) at the column outlet. Comparison of real (measurements) and simulated data for FOS and SGF.  It is of interest to assess the model parameter sensitivity by a perturbation method, i.e., by making small changes in the isotherm parameters and by observing the effect on the concentration profiles.  This sensitivity analysis is a first step towards a parameter estimation procedure, using the numerical simulator and minimizing the distance to the experimental data in some sense (the most common approach being the least-squares). This is subject of current work, and will be reported at the time of the conference.  CONCLUSIONS  Dowex Monosphere 99K/320 was found to be more suitable to work in the SMB unit as compared to Dowex 50W-X2 due to greater resistance at high pressure.  Batch experiments were carried out to estimate the adsorption parameters. The experimental results are compared with model prediction. The latter is computed by numerical solution of the mass balance equations of a kinetic model, using a method of lines approach and slope limiters for approximating the spatial operators. Indeed, very sharp concentration profiles travel trough the column and non-oscillatory schemes are necessary to avoid spurious oscillations and unrealistic negative concentration values.  REFERENCES  Ching, C. B., Ruthven, D. M. 1985. Experimental Study of a Simulated Counter-currrent adsorption system - III. Sorbex operation. Chemical Engineering Science, 40, 1411-1417. Gibson, G. R. 1998. Dietary modulation of the human gut microflora using prebiotics. British Journal of Nutrition, 80, S209-S212. Guiochon, G., Golshan- Shirazi, S., Katti, A. M. 1994. Fundamentals of preparative and nonlinear chromatography. Academic Press, 297-298. Gomes, P. S., Minceva, M., Rodrigues, A. E. 2006. Simulated moving bed technology: old and new. Adsorption-Journal of the International Adsorption Society, 12, 375-392. Luz, D. A., Rodrigues, A. K. O., Silva, F. R. C., Torres, A. E. B., Cavalcante, C. L., Brito, E. S., Azevedo, D. C. S. 2008. Adsorptive separation of fructose and glucose from an agroindustrial waste of cashew industry. Bioresource Technology, 99, 2455-2465. Nobre, C., Santos, M. J., Dominguez, A., Torres, D., Rocha, O., Peres, A. M., Rocha, I., Ferreira, E. C., Teixeira, J. A., & Rodrigues, L. R. (2009). Comparison of adsorption equilibrium of fructose, glucose and sucrose on potassium gel-type and macroporous sodium ion-exchange resins. Analytica Chimica Acta, 654, 71-76. Pedruzzi, I., da Silva, E. A. B., Rodrigues, A. E. 2008. Selection of resins, equilibrium and sorption kinetics of lactobionic acid, fructose, lactose and sorbitol. Separation and Purification Technology,. 63, 600-611. Tiihonen, J., Markkanen, I., Paatero, E. 2002. Complex stability of sugars and sugar alcohols with Na+, Ca2+, and La3+ in chromatographic separations using poly(styrene-co-divinylbenzene) resins and aqueous organic eluents. Chemical Engineering Communications, 189, 995-1008. Ruthven, D. M. 1984. Principles of adsorption and adsorption processes. John Wiley & Sons, New York. Wouwer, A. V., Saucez, P., Schiesser, W. E. 2004. Simulation of distributed parameter systems using a Matlab-based method of lines toolbox: Chemical engineering applications. Industrial & Engineering Chemistry Research,  43, 3469-3477.   ACKNOWLEDGEMENT  C. Nobre acknowledges the F.C.T. - Fundação para a Ciência e a Tecnologia (Portugal) for the PhD Grant ref. SFRH/BD/32514/2006. A. Severino is funded by Belgian Fund for Scientific Research (F.S.R.- FNRS).  This paper presents research results of the Belgian Network DYSCO (Dynamical Systems, Control, and Optimization), funded by the Interuniversity Attraction Poles Programme, initiated by the Belgian Federal Science Policy Oﬃce (BELSPO). The scientific responsibility rests with its authors.       0 5 10 15 20 25 30 35 40-10010203040506070time (s)RI1 signal  RI FOSRI SGFmeasurements

Operating conditions of a simulated moving bed chromatography unit for the purification of fructooligosaccharides

Operating conditions of a simulated moving bed chromatography unit for the purification of fructooligosaccharides

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