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Reducing support invasion in silicalite-1 membranes
2009 (English)Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
Abstract [en]

Zeolites are crystalline aluminosilicates with molecular sieving properties and are used in a variety of industrial processes such as catalysis, sorption and ion-exchange. Molecular sieving requires very dense membranes by its very nature, which is detrimental to the flux through the membrane. To ensure that high flux still can be achieved, the membranes made are very thin and placed on a porous support for mechanical stability. During synthesis, there is a significant risk of zeolite formation in the support pores, which reduces membrane efficiency. One method to prevent this so called support invasion is to use a two step masking method developed at Luleå University of Technology, which briefly can be described as covering the surface of the support with plastics (PMMA) and then filling the support pores with wax. This is followed by dissolving the PMMA and synthesizing the membrane with help of seed crystals on the now uncovered surface. After removing the wax by calcination, the membrane is ready for use. Recently, the reproducibility of the best membranes synthesized at Luleå University of Technology has been lower than normal and to determine the source of this quality drop, a thorough study was performed on the masking process. It was discovered that the wax did not impregnate the support properly, leaving the top layer of the support unmasked. After several experiments, it was discovered that most of the wax enters the support during repressurization back to atmospheric, after the supports have been placed upside down in molten wax and exposed to vacuum to remove the air in the support pores. To properly fill the support with wax, this repressurization needed to take more than five minutes. The increased repressurization time resulted in a significant improvement of the membrane quality: however the membranes did not achieve the same average quality as before. In the present work, it was also discovered that there were wax islands on the surface of the masked support, something previously not observed. It was prudent to assume that these wax islands and the remaining quality drop were interconnected. While the reason for their existence could not be solved in this work, several clues to their behaviour and importance were discovered, giving rise to possible solutions to the wax island problem to be investigated in future works. Finally it was investigated whether the currently used wax could be replaced, as the production of the current wax has ceased. This was shown to be possible and membranes of high quality were successfully prepared using wax from a different manufacturer.

Place, publisher, year, edition, pages
2009.
Keyword [en]
Physics Chemistry Maths, Silicalite, masking, support invasion, membrane
Keyword [sv]
Fysik, Kemi, Matematik
Identifiers
URN: urn:nbn:se:ltu:diva-50654ISRN: LTU-EX--09/139--SELocal ID: 7e451bdd-8046-42a9-9512-1ce9c082035eOAI: oai:DiVA.org:ltu-50654DiVA: diva2:1024016
Subject / course
Student thesis, at least 30 credits
Educational program
Chemical Engineering, master's level
Examiners
Note
Validerat; 20101217 (root)Available from: 2016-10-04 Created: 2016-10-04Bibliographically approved

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  • apa
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