HYDROPHOBIC COATINGS BASED ON COMMERCIAL PERFLUOROPOLYETHERS FOR FOULING MITIGATION. APPROACH ON A PILOT HEAT EXCHANGER PLANT

This work concerns the mitigation of fouling in heat exchangers, by means of the modification of the interaction between the foulant particles and the solid surfaces involved in the fouling phenomenon. To achieve this goal, hydrophobic coatings containing commercial perfluoropolyethers (PFPE) and metal oxides were prepared. Specifically, three typologies of coatings were prepared for the protection of stainless steel surfaces: commercial α,ω-inorganic substituted PFPE coatings, multilayer coatings containing the commercial PFPE and metal oxides nanopowders, and hybrid coatings containing sol-gel metal oxides networks and the commercial PFPE. All the coatings prepared were fully characterized in order to assess their morphology, composition and thickness. The wettability of the coatings was measured by contact angle (CA) determination, and all the coatings resulted to be hydrophobic, with CA>120°. The chemical and mechanical stability of all the coatings prepared was investigated by means of particular resistance tests, performed in liquid environments. Hybrid coatings appeared as the most resistant coatings against the erosion induced by chemical aggressive liquids, high temperature liquids (343 K), or shear stresses induced by the flowing of water upon the coated surface (0.17 m/s). The experimentation on a heat exchanger pilot plant confirmed the ability of the hydrophobic hybrid coatings to mitigate crystallization fouling on stainless steel heat transfer surfaces. In the condition adopted (transient flow regime and heat exchanging fluids at temperatures of 291-293 K and 318-323 K), the hybrid coating was able to delay the fouling step of about 200 hours and to promote the removal of the fouling deposits progressively formed on the heat transfer surfaces.