Development of a Multifunctional Membrane Process
Author
Hansen, Sebastian Lund
Term
4. Term
Education
Publication year
2021
Abstract
This thesis investigates the novel membrane process percrystallization (PCr), in which dry crystals form directly on the permeate side by balancing the rate of evaporation (RE) and the rate of permeation (RP). The aim was to define process requirements, compare polymeric and ceramic membranes, and assess whether controlled wetting can enable PCr with low-cost polymeric membranes. A lab-scale setup with hollow fiber/tubular modules, heated feed, vacuum, and a cold trap was used. Polypropylene (PP) membranes were activated using low surface tension liquids (isopropanol and the surfactant Triton X-100) under varied transmembrane pressure and vacuum, while an alumina-doped silica membrane was tested with NaCl and CuSO4. Stable, continuous production of dry NaCl and CuSO4 crystals was achieved with the ceramic membrane. The study shows that the RE/RP ratio is critical to process control, and that membrane properties and operating conditions (e.g., temperature and concentration) are key to tuning this ratio. For PP, establishing reproducible partial wetting that yielded an RP balanced with RE was challenging; alcohol caused rapid full wetting, whereas the surfactant produced more gradual wetting, yet consistent PCr was not achieved. The results confirm the feasibility of PCr with ceramic membranes and highlight the need for further work to robustly implement PCr with polymeric membranes and to refine RE/RP control.
Denne afhandling undersøger den nye membranproces perkrystallisering (PCr), hvor tørre krystaller dannes direkte på permeatsiden ved at balancere fordampningshastighed (RE) og permeationshastighed (RP). Formålet var at klarlægge proceskrav, sammenligne polymeriske og keramiske membraner og vurdere, om kontrolleret vædning kan muliggøre PCr med lavpris-polymermembraner. Et laboratorieopstil med hulfiber-/tubulære moduler, opvarmet føde, vakuum og koldfælde blev anvendt. Polypropylenmembraner (PP) blev aktiveret ved hjælp af lav-overfladespændingsvæsker (isopropanol og surfaktanten Triton X-100) under varierende transmembrant tryk og vakuum, mens en alumina-dopet silicahinde blev testet med NaCl og CuSO4. Der blev opnået stabil, kontinuerlig produktion af tørre NaCl- og CuSO4-krystaller med den keramiske membran. Undersøgelsen viser, at forholdet RE/RP er afgørende for en velfungerende proces, og at membranegenskaber samt driftsparametre (fx temperatur og koncentration) er nøglen til at styre dette forhold. For PP var det vanskeligt at etablere en reproducerbar, delvis vædning, der gav et RP i balance med RE; alkohol gav hurtig fuld vædning, mens surfaktant gav mere gradvis vædning, men konsistent PCr blev ikke opnået. Resultaterne bekræfter PCr’s gennemførlighed med keramiske membraner og peger på behov for yderligere arbejde med robust implementering i polymermembraner og præcis styring af RE/RP.
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