Matematičko modeliranje i istraživanje prijenosa mase u razvoju održivih biotehnoloških procesa proizvodnje organskih otapala i biogoriva

The aim of this work was to explore the possibility for development of the new, low-energy demanding process for bioethanol production directly from sugar beet cossettes. For that purpose a two-stage bioreactor system was assembled where the first stage was the vertical packed-bed column in order to use the vertical column in the first stage as an extracting column filled with the packed-bed of sugar beet cossettes that were extracted with concentrated suspension of baker’s yeast thus performing simultaneous extraction and fermentation. The second stage in a bioreactor system was a stirred tank bioreactor. The extraction of sugars was studied in 0,5 and 1,0 [m] column at extractant temperature of 20, 28, 36 and 72°C, respectively, by using two different residence times 24 and 49 [min]. Non-structured mathematical models of sugar extraction process were developed using linear, nonlinear and surface response regression methods as well as by the use of ternary plots. Also, the structured compartment type mathematical model for the sugar extraction from the sugar beet cossettes was established and explored in detail. The commercial baker’s yeast was the working microorganism in the simultaneous process of extraction and fermentation of sugar beet cossettes, thus it was subjected to the thorough fermentation kinetic analysis. Based on achieved results an own formal kinetic mathematical model for microbial conversion of sugars to ethanol (containing substrate and product inhibition terms) was developed and interconnected with the structured mathematical model of extraction (convection/diffusion mass transfer). This combined mathematical model was applied for the modelling of simultaneous extraction and fermentation of sugar beet cossettes in the two step bioreactor system. The model described correctly the new bioprocess and was able to predict values of parameters that have not been able to determine experimentally in those heterogeneous systems. It was proven that the model could be additionaly improved by the use of the computational fluid dynamics calculations.Cilj ovog rada bio je razvoj novog, energetski nisko zahtjevnog procesa proizvodnje bioetanola izravno iz rezanaca šećerne repe. U tu svrhu konstruiran je dvo-stupanjski bioreaktorski sustav (sastavljen od vertikalne kolone s nasutim slojem rezanaca šećerne repe koji je podvrgnut ekstrakciji s gustom suspenzijom pekarskog kvasca s kojom je provedena simultana ekstrakcija fermentacija. Drugi stupanj u bioreaktorskom sustavu bio je bioreaktor s miješalicom. Ekstrakcija šećera istraživana je u 0,5 i 1,0 [m] dugom vertikalnom cijevnom bioreaktoru na temperaturama od 20, 28, 36 i 72°C i kod dva vremena zadržavanja 24 te 49 minuta. Nestrukturirani matematički modeli ekstrakcije šećera su razvijeni korištenjem linearne i nelinearne regresije, metodom površinske regresije te korištenjem ternarnih dijagrama. Također je uspostavljen strukturirani kaskadni matematički model za ekstrakciju šećera iz rezanaca šećerne repe koji je detaljno istražen. Pekarski kvasac je korišten kao radni mikroorganizam u postupku simultane ekstrakcije i fermentacije te je stoga podvrgnut pažljivoj analizi kinetike fermentacije. Na temelju postignutih rezultata razvijen je vlastiti formalno kinetički matematički model za mikrobnuS konverziju šećera u etanol (koji sadrži članove za inhibiciju supstratom i produktom) koji je zatim povezan je sa strukturnim modelom ekstrakcije (konvektivni prijenos mase i molekulske difuzija). Ovaj složeni matematički model i primijenjen za modeliranje procesa simultane ekstrakcije i fermentacije rezanaca šećerne repe u bioreaktorskom sustavu od dva stupnja. Model je dobro opisivao novi bioproces te je mogao predviđati vrijednosti parametara koje nije bilo moguće eksperimentalno utvrditi u takovim heterogenim sustavima. Dokazano je da se model može dodatno unaprijediti s pomoću računalne dinamike fluida