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Experimentelle Untersuchung des Stofftransports im mikroblasenbegasten Rührreaktor unter der Berücksichtigung von Gegendiffusionseffekten
Citation Link: https://doi.org/10.15480/882.3546
Publikationstyp
Bachelor Thesis
Date Issued
2020-10
Sprache
German
Author(s)
Advisor
Referee
Matthes, Simon
Title Granting Institution
Technische Universität Hamburg
Place of Title Granting Institution
Hamburg
Examination Date
2020-10
Institut
TORE-DOI
TORE-URI
Citation
Technische Universität Hamburg (2020)
Many chemical and biological liquid phase reactions require gaseous components provided by aeration via gassed stirred tanks. For fast chemical and biological reactions mass transfer from the gas to the liquid phase is often limited making a continuous process optimisation necessary. For this process optimisation, the mass transfer is usually quantified in the laboratory via the volumetric mass transfer coefficient kLa using the measurement method of gas stripping with nitrogen.
The present work focuses on the characterisation of counter-diffusion effects and their influence on mass transport. The influence of different stripping gases on the determination of the kLa-value is particular important. The basis of this work is a 2 L stirred reactor and three gassing devices (opentube, L-sparger and sintered frit). These sparger can be differentiated primarily by their bubble size and shape. The analysis of mass transfer with different degassing methods is performed by the oxygen kLa-value for different gas volume flows and gassing devices. The reaction medium is stripped via nitrogen or argon. A physically degassed medium is used as well. In addition to mass transport measurements, endoscopic measurements are used to record the micro-bubbles generated by the sintered frit.
As a key-result of the investigations, the physically degassed medium shows 56% higher mass transport rates than the medium desorbed with nitrogen. The main reason is the counter-diffusion and the resulting lower oxygen partial pressure in the bubbles, which has a negative influence on the mass transport. Moreover, the counter-diffusion effects increase with higher gas solubility of the stripping gas and mass transfer rate of oxygen decreases.
In addition, the endoscopic measurement data and the kLa-values were used to calculate the respective mass transfer coefficients kL. These are characteristic for each degassing method. On the basis of the kLa-values a model for quantifying the counter-diffusion effects could be developed.
The present work focuses on the characterisation of counter-diffusion effects and their influence on mass transport. The influence of different stripping gases on the determination of the kLa-value is particular important. The basis of this work is a 2 L stirred reactor and three gassing devices (opentube, L-sparger and sintered frit). These sparger can be differentiated primarily by their bubble size and shape. The analysis of mass transfer with different degassing methods is performed by the oxygen kLa-value for different gas volume flows and gassing devices. The reaction medium is stripped via nitrogen or argon. A physically degassed medium is used as well. In addition to mass transport measurements, endoscopic measurements are used to record the micro-bubbles generated by the sintered frit.
As a key-result of the investigations, the physically degassed medium shows 56% higher mass transport rates than the medium desorbed with nitrogen. The main reason is the counter-diffusion and the resulting lower oxygen partial pressure in the bubbles, which has a negative influence on the mass transport. Moreover, the counter-diffusion effects increase with higher gas solubility of the stripping gas and mass transfer rate of oxygen decreases.
In addition, the endoscopic measurement data and the kLa-values were used to calculate the respective mass transfer coefficients kL. These are characteristic for each degassing method. On the basis of the kLa-values a model for quantifying the counter-diffusion effects could be developed.
Subjects
Gegendiffusion
volumetrischer Stoffübergangskoeffizient
Rührkessel
Mikroblasen
Entgasungsmethoden
DDC Class
600: Technik
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