Thin Organic‐Inorganic Anti‐Fouling Hybrid‐Films for Microreactor Components

Abstract

Deposit formation and fouling in reactors for polymer production and processing especially in microreactors is a well-known phenomenon. Despite the flow and pressure loss optimized static mixers, fouling occurs on the surfaces of the mixer elements. To improve the performance of such parts even further, stainless steel substrates are coated with ultra-thin films which have low surface energy, good adhesion, and high durability. Perfluorinated organosilane (FOTS) films deposited via chemical vapor deposition (CVD) are compared with FOTS containing zirconium oxide sol-gel films regarding the prevention of deposit formation and fouling during polymerization processes in microreactors. Both film structures led to anti-adhesive properties of microreactor component surfaces during aqueous poly(vinylpyrrolidone) (PVP) synthesis. To determine the morphology and surface chemistry of the coatings, different characterization methods such as X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR) spectroscopy as well as microscopic methods such as field-emission scanning electron microscopy (FE-SEM) and atomic force microscopy (AFM) are applied. The surface free energy and wetting properties are analyzed by means of contact angle measurements. The application of thin film-coated mixing elements in a microreactor demonstrates a significant lowering in pressure increase caused by a reduced deposit formation.

Monitoring Polymeric Fouling in a Continuous Reactor by Electrochemical Impedance Spectroscopy

“…1). This could also be shown in [28] for substrates exhibiting different roughness. Due to the O 2plasma treatment, the contact angle decreased again to 54°.…”

“…After application of the [ZrO x /FOTS] II film, the surface hydrophobicity could be restored. Also, the surface free energy of 23.3 mN m -1 (g p = 1.2 mN m -1 , g d = 22.1 mN m -1 ), as measured by contact angle determination under variation of liquids with different polar and dispersive components, lies in a similar range to the respective single coated surface in [28]. This implies similar surface wetting properties.…”

“…The FOTS-containing ZrO x films were applied to the surfaces by sol-gel method as published by Izumi et al [29]. The deposition procedure of the first hybrid film layer onto polished stainless steel (referred to as single ZrO x /FOTS deposition ([ZrO x /FOTS] I ) was recently published [28]. Prior to the application of the second film (referred to as double ZrO x /FOTS coating ([ZrO x /FOTS] II ), a plasma treatment was carried out.…”

Validation of an Extended Kinetic Model of Free‐RadicalN‐Vinylpyrrolidone Polymerization

“…[ 8–11 ] One way to avoid or reduce fouling in microreactors is the choice of suitable coatings. [ 4,12,13 ]…”

“…[8][9][10][11] One way to avoid or reduce fouling in microreactors is the choice of suitable coatings. [4,12,13] Fouling may also be reduced by a suitable choice of operation conditions and mixer geometry using a kinetic model, [2,14] which predicts the microstructure of the resulting polymers. The reaction mechanism of the radical polymerization of NVP in aqueous solutions has been studied in several publications.…”