Turbulence promoting microstructures inside hollow fiber membranes by a rotation-in-a-spinneret process

  • Erzeugung von turbulenzfördernden Mikrostrukturen in Hohlfasermembranen durch einen Rotation-in-a-Spinneret Prozess

Tepper, Maik; Wessling, Matthias (Thesis advisor); Çulfaz-Emecen, Zeynep (Thesis advisor)

Aachen : Aachener Verfahrenstechnik (2023)
Book, Dissertation / PhD Thesis

In: Aachener Verfahrenstechnik series - AVT.CVT - chemical process engineering 40
Page(s)/Article-Nr.: 1 Online-Ressource : Illustrationen, Diagramme

Dissertation, Rheinisch-Westfälische Technische Hochschule Aachen, 2023

Abstract

Membranes are semi-permeable barriers to control mass transport and enable chemical separation processes on a molecular level. Focus areas of hollow fiber membrane technology include water treatment, food and beverage processing, gas separation and medical applications. Intense membrane research has succeeded in developing better membrane materials with improved permeability and selectivity. Simultaneously, such improvements introduce concentration polarization effects in operation, which causes productivity limitations. However, generating local turbulence promotion is proven to counteract such limitations by introducing mixing and mass transfer enhancement. Hence, this thesis aims to develop a scalable spinning methodology to incorporate turbulence promoting microstructures inside hollow fiber membranes in a single production step. Therefore, this thesis presents the novel Rotation-in-a-Spinneret platform technology combined with customized 3D printed microstructured spinnerets. Wet spinning with phase inversion was the basic fabrication technique to produce microporous polyethersulfone (PES) and polyvinylidene fluoride (PVDF) hollow fiber membranes. The principal spinneret design concept featured a microstructured spinneret orifice for shaping the desired hollow fiber microstructure. In addition, implementing rotation of said feature enabled simultaneously twisting the microstructure helical. In particular, this thesis presents three approaches to implement rotation in a spinneret. Such are rotation of the entire spinneret, the bore needle and a novel component in the spinneret center. As a result, the two membrane concepts Helical-Ridge-Membranes and Static-Mixer-Membranes emerged. Helical-Ridge-Membranes exhibit helical ridges incorporated into the selective lumen surface. For their fabrication, the spinneret’s microstructured bore needle features a grooved orifice that initiated helical ridge formation upon needle rotation. Static-Mixer-Membranes highlight a membrane system combining a hollow fiber membrane with a twisted tape static mixer. The rotating spinneret simultaneously fabricated and integrated a static mixer inside a hollow fiber membrane. The static mixer evolved by co-extrusion of a second polymer solution through a rotating microstructured needle, directly into the lumen of the nascent hollow fiber membrane. Specifically designed rotating spinning parameters enabled engineering helical microstructures with an adjustable shape, pitch and pitch direction. Investigating membrane geometry and analyzing characteristic membrane properties elucidated the interplay between spinneret rotation and membrane formation. Furthermore, experimental and simulative studies proved the evolution of secondary flow patterns. Ultimately, the turbulence promoting membranes realized up to 10-fold mass transfer enhancement in colloidal filtration and gas-liquid membrane contactor applications. Thus, the microstructured hollow fiber membranes introduced turbulence promotion for mass transfer enhancement. Moreover, the concepts effectively minimized concentration polarization at the membrane surface to establish energy-efficient membrane processes.

Institutions

  • Chair of Chemical Process Engineering and Institute of Process Engineering [416110]

Identifier

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