Modeling of the fermentation in an internal loop airlift reactor

Transcription

1 17 th Euopean Symposium on Compute Aided Pocess Engineeing ESCAPE17 V. Plesu and P.S. Agachi (Editos) 7 Elsevie B.V. All ights eseved. 1 Modeling of the fementation in an intenal loop ailift eacto Ivan Sikula, Matin Juaščík, Jozef Makoš Institute of Chemical and Envionmental Engineeing Faculty of Chemical and Food Technology Slovak Univesity of Technology,Radlinského 9, Batislava 81 37, Slovakia, jozef.makos@stuba.sk Abstact The ailift eactos have potential application in biotechnology industies due to thei simple constuction and less shea stess imposed on shea sensitive cells compaed with the mechanically stied tanks. This wok was focused on mathematical modeling of the fementation pocess in an intenal loop ailift eacto (IAR). Simulation esults wee veified on the fementation of the gluconic acid by the stain Aspegillus nige which has been chosen as a model system. The fementation was caied out in thee laboatoy IARs (each one with diffeent scale: 1, 4 and dm 3, espectively) and pefomed in gowth o non-gowth conditions. Model of the IAR incopoated the mateial balance of each compound taking pat in eaction. In the eacto thee ae ecognized fou main pats: bottom, ise, sepaato and downcome. Each zone of that eacto was modeled sepaately due to the diffeent flow patten and the mixing behavio. Paametes of the model, such as mass tansfe coefficient of oxygen, gas holdups, and ciculation velocities, wee pedicted using expeimentally detemined coelations. The esults of the simulations and expeiments ae in sufficient ageement. Keywods Ailift bioeacto, gluconic acid fementation, mathematical modeling, scale-up

2 I. Sikula et al. 1. Intoduction In biopocesses thee is still pefeable most common stied tank eacto (STR). A choice of the pope type of eacto depends on the chaacte of the biosystem. Ailift eactos (AR) could be moe convenient than STRs in pocesses whee the low shea stess is involved using a shea sensitive stains. Mixing in ARs is povided by expansion of the gas enteing the eacto, hence thee is no need to use an additional stie and consequently exta enegy souce. This could be moe advantageous fo poduction of high volume poducts with elatively low added value. Nevetheless, the utilization of ARs is still limited fo the sake of insufficient infomation about pope scale-up pocedue.. Poblem Statement, backgound Mixing in ARs is usually impefect. Fom the mixing point of view, fou main sections in ARs ae ecognized: the bottom whee the gas distibuto is placed and the medium is ecycled fom the downcome, the ise (in the intenal loop AR (IAR) a concentic tube), whee the medium flows upwad, the gas sepaato and the downcome. Each section is usually modeled sepaately. Thee ae two majo appoaches fo modeling these sections: the axial dispesion model (ADM) and the tanks in seies model (TSM) [1, ]. In ou case we chose TSM. 3. Appoach on modeling of IAR 3.1. Mathematical model of IAR The mathematical model of an IAR was developed by dividing the whole eacto into a system of ideal tanks in seies (see Figue 1). In each tank of the AR, mateial balances wee witten fo the liquid and the gas phase. Geneally, a simple scheme of the balance fo a compound in a tank can be witten by Eq.(1). Mathematically it pesents a set of odinay diffeential equations with coesponding initial conditions. ate of accumulation of inlet of a compound outlet of a compound = - + a compound in the tank to the tank fom the tank (1) intephase tansfe of poduction ( consumption) + + a compound to the tank ate of a compoundin the tank

3 Modeling of the fementation in an intenal loop ailift eacto 3 Figue 1 Schematic diagam of the tanks in seies model fo an AR. 3.. Model paametes estimation Solution of the model equations equies a pope estimation of thei paametes. These paametes that ae elated with hydodynamics of the eacto (gas hold-ups in all sections, volumetic oxygen mass tansfe coefficients, ciculation velocities), wee detemined on ou devices using model media. The solubility of oxygen is function of the pessue along the AR and media composition [3, 4], what was taken into account Model eaction and kinetics As a model system, gluconic acid poduction by the stain Aspegillus nige was chosen. The liquid phase with the pellets of the micooganism was teated as pseudo-homogeneous. Biotansfomation of glucose (Glc) to gluconic acid (Glu) by the filamentous fungi Aspegillus nige epesents a simple dehydogenation eaction without involvement of complex metabolic cell pathways [5]. The oveall eaction of biotansfomation can be witten as follows: Glucose-oxidase Glc+ 1 O Glu (A) Catalase The expessions fo the gowth ates of the biomass X, the poduction ate of the poduct P, the substate consumption ate S and the oxygen uptake ate O ae efeed to equations given in Table 1.

4 4 I. Sikula et al. Table 1 Kinetic equations micobial gowth ate Gowth conditions cs co X = μm c X KScX + cs KOcX + co Non-gowth conditions X = poduction ate of the poduct The 1 dm 3 IAR was used fo the detemination of kinetic paametes. Accoding to a elatively slow eaction and sufficient mixing [6, 7], this eacto was assumed to be a CSTR. Estimation of the kinetic paametes μ m, K S, K O, V m, K PS, K PO, α and γ fo the gluconic acid poduction was done by using expeimental data of the gowth fementation. Paametes β and δ wee detemined fom the stoichiomety of eaction (A). The estimated values of kinetic paametes ae pesented in Table. Table Estimated kinetic paametes μ m K S K O 1 4 V m K PS K PO 1 3 α β γ δ (h -1 ) (-) (-) (h -1 ) (g dm -3 ) (g dm -3 ) (-) (-) (-) (-) Expeimental aangement Details about the micooganism and cultivation conditions as well as geomety and analytical methods and contol of the eactos duing fementation ae descibed in ou pevious pape [5]. Hydodynamic measuements (gas hold-up, ciculation velocities, ciculation egimes chaacteization and volumetic mass tansfe coefficient) ae in detail epoted in the papes of Klein et al. [8], Blažej et al. [6, 9] and Juaščík et al. [1]. 4. Results V c m X P = KPS KPO 1+ + cs co substate consumption ate S αx βp oxygen consumption ate O γ X δ P The developed mathematical model of an IAR was expeimentally veified on 4 dm 3 and dm 3 eactos in gowth o non-gowth conditions. All expeiments stated at the same initial concentation of glucose (equal to = S = βp = O = δ P V c m X P = KPS KPO 1+ + cs co

5 Modeling of the fementation in an intenal loop ailift eacto 5 15 g dm -3 ) and in case of gowth fementation with defined concentations of othe nutients equied fo the micobial gowth. All simulations wee povided by employing the kinetic paametes estimated by using the data fom the 1 dm 3 IAR (Table ) Scale-up simulations The gowth fementation in dm 3 IAR at constant aeation of V in G = 6 dm 3 h -1 is shown in Figue. Model data well descibe the expeimental couses of glucose, biomass and poduct. In the Figue 3 thee can be seen coesponding oxygen couses along at 5 th hou of the fementation time in the same eacto. The concentation of dissolved oxygen eaches the maximum in the ise section of the IAR. The slope of that cuve is changing accoding to the oxygen mass tansfe diving foce.,, Figue Model vs. expeimental data of the gowth fementation in the dm 3 IAR (c X =.34 g dm 3 ) c X exp c X exp exp exp t / h t / h Figue 4 Non-gowth fementation in 4 dm 3 IAR at vaious aeations (c X =.1 g dm -3 ). exp G exp (.1 4 ) / (g dm -3 ) c X 4.1 G / (dm 3 h -1 ), Figue 3 Oxygen pofile in liquid and gas phase at 5 th hou of fementation time in the dm 3 IAR. Figue 5 Non-gowth fementation in dm 3 IAR at vaious aeations (c X = 5.9 g dm -3 ). In anothe set of expeiments in 4 dm 3 and dm 3 IARs thee was studied the effect of aeation on the Glu poduction. These expeiments wee povided at non-gowth conditions. Results ae pesented in the Figue 4 and Y O t / h N exp exp G exp (.1 3 ) / (g dm -3 ) Y O h -1 ) G / (dm 3

6 6 I. Sikula et al. The expeiments in 4 and dm 3 eactos wee opeated in ange of volumetic gas flow fom 1 to 4 dm 3 h -1 and fom 1 to 1 dm 3 h -1 espectively. Model data fo the Glc and Glu ae in a good ageement with those expeimental. Highe diffeence between the values of measued dissolved oxygen data and model esults could be explained by the pesence of ai bubbles on the oxygen pobe membane and by the accuacy of detemination of dy biomass weight concentation in the medium. It is obvious that this model is able to pedict the effect of changes in aeation on ate of Glu poduction. In the futue this model could be a useful tool fo the design and scaleup of industial applications of IARs. ist of symbols c concentation [g dm -3 ] K O, K S limitation constant of oxygen and substate fo the poduct [g dm -3 ] K PO, K PS limitation constant of oxygen and substate fo the biomass [ ] eaction ate [g dm -3 h -1 ] V m, μ m maximum specific ate fo the poduct and gowth [h -1 ] V in G volumetic gas flow [dm 3 h -1 ] Y mola faction [ ] α,γ gowth associated glucose and oxygen consumption coefficient [ ] β,δ on-gowth associated glucose and oxygen consumption coefficient [ ] G,, liquid, gas, initial O, P, S, X oxygen, gluconic acid, glucose, biomass Acknowledgements This wok was suppoted by the Slovak Scientific Gand Agency, gant numbe VEGA 1/3573/6. Refeences 1. uttmann R., Thoma M., Buchholz H., Schugel K., Comput. Chem. Eng., 7 (1983) 43.. Adle I., Deckwe W. D., Schugel K., Chem. Eng. Sci., 37 (198) Schumpe A., Chem. Eng. Sci., 48 (1993) Rischbiete E., Schumpe A., Wunde V., J. Chem. Eng. Data, 41 (1996) Klein J., Rosenbeg M., Makoš J., Dolgoš O., Košlák M., Kištofíková Ľ., Biochem. Eng. J., 1 () Blažej M., Kiša M., Makoš J., Chem. Eng. Pocess., 43 (4) Andé G., Robinson C. W., Moo-Young M., Chem. Eng. Sci., 38 (1983) Klein J., Dolgoš O., Godó Š., Blažej M., Makoš J., Chem. Pap., 54 () Blažej M., Annus J., Makoš J., Chem. Pap., 57 (3) Juaščík M., Blažej M., Annus J., Makoš J., Chem. Eng. J., 15 (6) 81.