Synthesis and Filtration Dewatering of Model Colloids in the μm Range
Translated title
Syntese og Afvandingsfiltrering af Modelcolloider i μm størrelsen
Author
Lorenzen, Søren
Term
4. term
Education
Publication year
2012
Submitted on
2012-05-31
Pages
59
Abstract
Membranfiltrering kræver ofte modeller, der beskriver, hvordan suspenderede faste stoffer interagerer med membranen. Mange udbredte modeller bygger på forsøg med uorganiske partikler og fanger derfor ikke adfærden i komplekse systemer som kommunalt og industrielt spildevand. Her danner organiske faste stoffer filterkager, der kan være både sammenpresselige og negativt ladede, hvilket påvirker gennemstrømningen. For at forbedre modellerne er der behov for organiske partikler med kontrollerbare egenskaber. Dette arbejde undersøger dispersionspolymerisation som metode til at fremstille sådanne partikler: methylmethacrylat med polyvinylpyrrolidon (PVP) som stabilisator og styren med poly(akrylsyre). Første del kombinerer litteratur og forsøg for at beskrive den anvendte polymerisation. Anden del udfører dead-end afvandsningsfiltrering af de fremstillede partikler, gennemgår de mest brugte matematiske modeller til at forudsige den specifikke filtreringsmodstand, α (et mål for hvor svært væsken passerer gennem filterkagen), og sammenligner forudsigelserne med målingerne. Resultaterne viser, at α for methylmethacrylat/PVP-partikler ligger tæt på de forudsagte værdier, mens α er markant højere for styren/poly(akrylsyre)-partikler, sandsynligvis på grund af interaktioner mellem de ladede partikeloverflader og det omgivende vand. Kun én partikeltype udviste en svag trykafhængighed af α, og kun ved længere filtreringstider (større filtrerede volumener). Dette kan skyldes tilsætning af en overfladeaktiv monomer under syntesen, som øger det lokale osmotiske tryk omkring partiklerne. Ved blanding af små og store partikler dominerede de små modstanden, formentlig fordi de fylder hulrummene mellem de store og tilstopper strømvejene.
Membrane filtration often relies on models that describe how suspended solids interact with the membrane. Many commonly used models are based on tests with inorganic particles and therefore do not capture the behavior of complex streams such as municipal and industrial wastewater. In these systems, organic solids form filter cakes that can be both compressible and negatively charged, which affects flow. To improve such models, there is a need for organic particles with controllable properties. This thesis studies dispersion polymerization as a way to make these particles: methyl methacrylate with polyvinylpyrrolidone (PVP) as stabilizer, and styrene with poly(acrylic acid). The first part combines literature and experiments to describe the polymerization process. The second part performs dead-end dewatering filtration of the produced particles, reviews the most used mathematical models to predict the specific resistance to filtration, α (a standard measure of how difficult it is for liquid to pass through the filter cake), and compares predictions with measurements. The results show that α for methyl methacrylate/PVP particles is close to the predicted values, while α is significantly higher for styrene/poly(acrylic acid) particles, likely due to interactions between the charged particle surfaces and the surrounding water. Only one particle type showed a slight pressure dependence of α, and only at longer filtration times (larger filtered volumes). This may be caused by the addition of a surface-active monomer during synthesis, which increases the local osmotic pressure around the particles. When small and large particles were mixed, resistance was mainly governed by the smaller ones, likely because they fill the voids between the larger particles and block flow.
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