- Titel
- Mass transfer during biopolymer aerogel production
- Untertitel
- measurement and modeling
- Zitierfähige Url:
- https://nbn-resolving.org/urn:nbn:de:bsz:105-qucosa2-949639
- Datum der Einreichung
- 18.03.2024
- Datum der Verteidigung
- 30.08.2024
- Abstract (EN)
- This thesis aims to measure and model diffusive mass transfer processes during all three steps of biopolymer aerogel production using 1-D Raman spectroscopy: gelation in aqueous media, solvent exchange to an organic solvent, and supercritical drying using CO2. For the gelation step, the CO2 induced gelation of pectin gels was investigated. It could be shown that the liquid gelling solution likely solidifies immediately upon contact with CO2 and that therefore diffusion is the only relevant mass transfer mechanism. Solvent exchange and supercritical drying of cylindrical gel monoliths were exemplarily analyzed using agar and whey protein isolate gels. A convective mass transfer model that includes both, diffusion and advection due to volume changes upon mixing was implemented with the effective diffusion coefficient being the sole fit parameter. It was shown that advection can play a decisive role during supercritical drying due to the high excess volume of the CO2+EtOH system. In order to calculate the excess volume during supercritical drying, non-saturated binary mixture densities were experimentally determined for the four binary systems of CO2+EtOH, acetone, acetonitrile and DMSO from 308-333 K and 6-12 MPa over the whole composition range in the single-phase region. Tortuosity factors derived from the experimentally determined effective diffusion coefficients during solvent exchange and supercritical drying differed by a factor of two, although the gels did not show any shrinkage. This contradiction could be attributed to an incorrect prediction of the binary diffusion coefficient of EtOH+CO2 in common aerogel literature. Stepwise supercritical drying was then employed to experimentally analyze the true composition dependency of the binary diffusion coefficient of EtOH+CO2. Especially when solvent exchange is performed in onesingle step, unwanted shrinkage of the gel matrix can occur. It was shown that shrinkage leads to a heterogeneous density distribution of the gel network with a compaction towards its center. Most of the shrinkage takes place during the very beginning of solvent exchange when EtOH can be detected in the outermost layers only and that further shrinkage is prevented by a sharp increase in gels stiffness.
- Verweis
- Protein gel shrinkage during solvent exchange: Quantification of gel compaction, mass transfer and compressive strength
DOI: 10.1016/j.foodhyd.2021.106916 - Non-saturated mixture densities of the binary systems of carbon dioxide and the organic solvents ethanol, acetone, acetonitrile and dimethyl sulfoxide from 6-12 MPa
DOI: 10.1016/j.fluid.2021.113201 - Mass transfer kinetics inside bio-(aero)gels during solvent exchange and supercritical drying: On the relevance of advection, gel-porosity and a peculiarity regarding the tortuosity
DOI: 10.1016/j.supflu.2022.105762 - CO2 induced gelation of amidated pectin solutions: Impact of viscosity and gel formation
DOI: 10.1016/j.cherd.2022.02.012 - Freie Schlagwörter (DE)
- Aerogele, Lösungsmittelaustausch, überkritische Trocknung, Raman-Spektroskopie
- Freie Schlagwörter (EN)
- Aerogels, solvent exchange, supercritical drying, Raman spectroscopy
- Klassifikation (DDC)
- 660
- Normschlagwörter (GND)
- Aerogel
- Trocknung
- Lösungsmittel
- Tortuosität
- Raman-Spektroskopie
- GutachterIn
- Prof. Dr. Andreas Bräuer
- Dr. Pavel Gurikov
- BetreuerIn Hochschule / Universität
- Prof. Dr. Andreas Bräuer
- Den akademischen Grad verleihende / prüfende Institution
- Technische Universität Bergakademie Freiberg, Freiberg
- Version / Begutachtungsstatus
- publizierte Version / Verlagsversion
- URN Qucosa
- urn:nbn:de:bsz:105-qucosa2-949639
- Veröffentlichungsdatum Qucosa
- 05.02.2025
- Dokumenttyp
- Dissertation
- Sprache des Dokumentes
- Englisch
- Lizenz / Rechtehinweis
CC BY-NC-ND 4.0