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PhD topics for academic year 2021/2022

Department of Chemical Engineering

Chemical and Process Engineering

Faculty of Chemical Engineering

Gas - Liquid Mass Transfer. Experimental comparison of various apparatuses performance.

Moucha Tomáš, prof. Dr. Ing. ( mou...@vscht.cz)
The volumetric mass transfer coefficient (kLa) plays a crucial role in industrial design in the case of the process controlled by gas–liquid mass transfer. Prediction of kLa is nowadays mostly based on literature correlations. Our research goal is to establish suitable kLa correlations for different types of devices that would be based on the experimental dataset. The PhD thesis aim at the comparison of various gas-liquid contactor types from the viewpoint of their mass transfer efficiency. The suitable correlations will be developed that would be viable for mechanically agitated gas–liquid contactors and also for pneumatically agitated gas–liquid contactors such as airlift reactor.
Development principles: 1. Get familiar with mathematical descriptions of a gas-liquid interfacial mass transfer including mass balances of various gas-liquid contactor types
2. Study mathematical models of the mass transport which enable the determination of gas-liquid mass transfer coefficients from experimental data
3. Get to know the experimental apparatuses available at UNIPA in the working group of prof. Brucato and prof. Scargiali as well as those at UCT Prague in the Mass Transfer Laboratory
4. Build the experimental plan which will ensure obtaining experimental results to compare the effectivity of individual apparatuses according to the criteria selected
5. Theoretical findings, experimental procedures and results as well as the conclusions formulated write in the dissertation
Faculty of Chemical Engineering

KLa - shear stress coupling to design fermenters better

Moucha Tomáš, prof. Dr. Ing. ( mou...@vscht.cz)
In fermentation technologies, mechanically agitated aerated vessels are frequently used. In cases of aerobic fermentations, the Oxygen Uptake Rate - OUR is frequently used as the important design parameter. This means that the gas-liquid mass transfer controlled process is considered and the volumetric mass transfer coefficient - kLa is taken as the most important parameter. The practice shows, however, that the impellers with lower Power number (which means lower turbulence intensity and lower kLa) often ensure higher bioprocess efficiency than those with high Power number (which means higher turbulence intensity and higher kLa). The explanation is brought by the fact that microorganisms/biomass might be damaged by the high turbulence intensity as explained further. The turbulence intensity is proportional to shear stresses occuring in the mechanically agitated fermentation batch. A high shear stress may "cut" the microorganisms, which stop producing their primary product then. The aim of the PhD thesis is to measure the quantities proportional to shear stress values at the process conditions of aerobic fermentations and couple them with the kLa values, which are already at disposal in the Mass Transfer Lab database at UCT Prague. This data coupling will enable to develope the highly efficient industrial fermenters design tool.
Development principles: 1. Get familiar with the description of the gas-liquid mass transfer in mechanically agitated dispersions.
2. Get familiar with the descritpion of local turbulence intensities., fluctuation velocities and shear stresses in mechanically agitated gas-liquid disperions.
3. Study experimental techniques of kLa measurement in UCT Mass transfer Laboratory and of the quantities proportional to the local turbulence intensity used at TU Berlin.
4. Study the eperimental conditions used in Mass Transfer Laboratory at UCT Prague to obtain kLa database and then, at the same conditions measure the quantities proportional to local turbulence intensities as used at TU Berlin.
5. Complete the kLa database by the quantities usable to compute shear stresses and suggest the way how to use these coupled data in industrial fermenters design.
Faculty of Chemical Engineering

Characterization and modelling of dispersion systems with variable viscosity

Šoóš Miroslav, prof. Ing. Ph.D. ( Mir...@vscht.cz)
Kuhn Simon, Prof. Dr. ( sim...@kuleuven.be)
The goal of this project is to characterize and model systems where viscosity of the dispersed phase is rising during the process. Typical examples are emulsification, suspension polymerization or spherical agglomeration. The student will start with simplified system composed of two liquid phases with various viscosities, which will be analyzed by on-line sensors providing information about the droplets sizes. Experimental activity will cover both batch as well as continuous operation modes. Collected data will be consequently used to develop engineering model based on computational fluid dynamic of the fluid flow coupled with population balances to describe coalescence and breakup of dispersed phase for various levels of dispersed phase viscosity. An extension of this activity will be process of spherical agglomeration where dispersed phase will contain particles (nanoparticles or crystals), which can undergo agglomeration and thus increasing the viscosity of the dispersed phase. Developed model will be validated against experimental data collected at various scales or operating conditions.
KU Leuven, Belgium
Faculty of Chemical Engineering

Polymer-based membranes for highly selective removal of CO2 from biogas

Kočí Petr, doc. Ing. Ph.D. ( pet...@vscht.cz)
Vankelecom Ivo, prof. ( ivo...@kuleuven.be)
Membrane-based gas separation technology has contributed significantly to the development of energy-efficient systems for natural gas purification. Also CO2 removal from biogas, with CO2 contents exceeding 40% has more recently known rapid growth and development. Major challenge of polymer membranes for gas separation is related to their susceptibility to plasticization at high CO2 partial pressures. CO2 excessively swells the polymer and eases the permeation of CH4, thus reducing the selectivity. Membrane crosslinking is one of the best ways to prevent the plasticization. Mixed matrix membranes (MMMs), consisting of fillers homogeneously dispersed in a polymeric matrix aim at combining the processibility of polymers and the superior separation properties of the porous fillers. Metal-organic frameworks (MOFs) are such materials which have attracted considerable attention due to their tailorable functionality, well-defined pore size, pore tunability and breathing effects. MMMs for biogas upgrading will be prepared with increased permeabilities by choosing proper MOF/polymer combinations and modifying the thermal treatment, employing core-shell MOF materials with high bulk porosity and a selective shell layer.

KU Leuven, Belgium
Faculty of Chemical Engineering

Solvent and pH stable membranes with ultra-sharp molecular weight cut-off values

Kočí Petr, doc. Ing. Ph.D. ( pet...@vscht.cz)
Vankelecom Ivo, prof. ( ivo...@kuleuven.be)
Membrane-based separations currently offer the best strategy to decrease energy requirements and environmental footprint through newly developed solvent resistant nanofiltration (SRNF) or solvent-tolerant nanofiltration (STNF). So-called solvent activation of polymeric membranes involves treatment of an existing membrane by contacting it with solvents or solvent mixtures, which is hypothesized to restructure the membrane polymer through solvatation, increase polymer chain flexibility and organization into suitable structures. This will be verified by systematically treating membranes with different solvents and testing them for the separation of synthetic liquid streams. A high-throughput set-up will be used. Fundamental physico-chemical characterisations of the membranes before and after the treatments will provide insight in the changes at molecular level. The characterization techniques include gas and liquid uptake experiments (diffusivity), PALS (positron annihilation lifetime spectroscopy, to determine free volume element distributions), ERD (elastic recoil scattering, providing elemental analysis in membrane depth profiles), solid state NMR (nuclear magnetic resonance), TGA (thermogravimetric analysis) and DSC (differential scanning calorimetry).

KU Leuven, Belgium
Updated: 29.11.2019 12:30, Author: Jan Kříž

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