On the Morphological Characterization Procedures of Multilayer Hydrophobic Ceramic Membranes for Membrane Distillation Operations.

Mohamed Fawzy,Serena Bandini,Felipe Varela-Corredor

doi:10.3390/membranes9100125

Mohamed Fawzy, Serena Bandini + Show 1 more

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https://doi.org/10.3390/membranes9100125

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Journal: Membranes	Publication Date: Sep 23, 2019
Citations: 4	License type: CC BY 4.0

Affiliation: University of Bologna

Abstract

The paper introduces some aspects of the characterization of hydrophobized multilayer ceramic membranes intended for use in membrane distillation (MD) operations. Four-layer hydrophobic carbon-based titania membranes, manufactured by the Fraunhofer Institute for Ceramic Technologies and Systems (IKTS, Hermsdorf, Germany), were tested according to the gas permeation technique. Gas permeance data were elaborated following the premises of the dusty gas model, to calculate the average pore size and the porosity-tortuosity ratio of each layer. Membrane testing was the opportunity to discuss which characterization method is more appropriate to obtain the membrane parameters necessary for the simulation of membranes in MD processes. In the case of multilayer membranes, the calculation of the morphological parameters should be performed for each layer. The “layer-by-layer gas permeation” method, previously introduced by other authors and completed in this work, is more appropriate for obtaining representative parameters of the membrane. Conversely, the calculation of morphological parameters, averaged over the entire membrane, might lead to heavy underestimations of the total membrane resistance and then to a heavy error on the transmembrane flux simulation.

Highlights

Since the beginning of the 1980s it has been well known that membrane distillation (MD) for aqueous solutions can operate with membrane contactors (MC) containing hydrophobic macroporous membranes [1,2]
Membranes are required with an average pore diameter in the range from 20 to 200 nm, manufactured with hydrophobic materials able to guarantee minimum liquid entry pressure (LEPmin ) values at room temperature not lower than nearly 1 bar, to have a safety margin for industrial applications at higher temperatures
The main drawback for their application in MD is their hydrophilicity; it can be circumvented by the modification of the top layer by polymer grafting and/or carbonization techniques

Summary

Introduction

Since the beginning of the 1980s it has been well known that membrane distillation (MD) for aqueous solutions can operate with membrane contactors (MC) containing hydrophobic macroporous membranes [1,2]. Membranes are required with an average pore diameter in the range from 20 to 200 nm, manufactured with hydrophobic materials able to guarantee minimum liquid entry pressure (LEPmin ) values at room temperature not lower than nearly 1 bar, to have a safety margin for industrial applications at higher temperatures. There has been a growing interest among the scientific community in the application of ceramic membranes for MD, owing to their high thermal and chemical stability; such materials might give greater morphological stability than polymeric membranes over time [3]. Ceramic membranes are typically asymmetrical, formed by the deposition of different layers made of γ-alumina and/or titania and/or zirconia and/or silica or a combination of them. Patents [4,5]

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