Abstract
Hydrophobic porous metallic membranes can be integrated in a microreactor for in situ separation of steam at high temperatures. This study investigates the fabrication and characterization of hydrophobic coatings on metallic substrates. Two different coating methods were explored: (1) Plasma Enhanced—Chemical Vapor Deposition (PE-CVD) to form amorphous carbon silicon-doped a-C:H:Si:O thin films and (2) Direct Immersion in fluoroalkyl silane (FAS-13) solution using dip coating to form Self-Assembled Monolayers. The results on wettability as well as SEM images and EDS/WDS analyses indicate that the coated sintered stainless steel membranes are adequate as hydrophobic surfaces, maintaining the porosity of the substrate and withstanding high temperatures. Especially the FAS-13 coating shows very good resistance to temperatures higher than 250 °C. These findings are of special significance for the fabrication of porous metal membranes for separation of steam in high temperature applications.
Highlights
Process intensification in microstructured devices can be pursued by combining in situ two unit operations: chemical reaction and separation
Amorphous diamondlike carbon (DLC) thin film layers doped with silicon and oxygen (a-C:H:Si:O) were deposited using a combined PVD/PECVD System (STARON 60-60, PT&B Silcor) at 180 ◦ C and 1.5 Pa chamber pressure operated with a radiofrequency power of the plasma source of 100 W
The coating thickness, morphology, and quality of the surface were analyzed by Scanning Electron Microscopy and profilometry
Summary
Process intensification in microstructured devices can be pursued by combining in situ two unit operations: chemical reaction and separation. The membrane should be hydrophobic to block the passage of the target product (aqueous reactive solution) while allowing water in vapor state to enter the pores. This specific polycondensation reaction, when performed in a microreactor with short and well defined residence time, needs rather high temperatures (230–250 ◦ C) for obtaining high yield and selectivity. Such high temperatures imply several challenges for the membrane, like the adequacy of the material for the reaction conditions and suitable surface properties to prevent the reaction product from entering the pores [1].
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