Improvement of the anticorrosive and thermal properties of an Epoxy-SiO2 coating due to the presence of silicon nitride

In recent years there has been a significant boom in the production of biofuels, especially biomethane, through anaerobic biodigestion, but when the substrates decompose inside the reactors, they generate hydrogen sulfide, H2S as a byproduct. On the other hand, to increase the efficiency of biodigesters it is necessary to have control of temperature. Based on our experience, one of the ways to achieve that control is to take the gas from the upper part of the reactor, pass it through a solar heat exchanger, and then inject the hot gas in the bottom of the reactor. However, gas recirculation results in corrosion of copper pipes due to the high hydrogen sulfide, H2S content of the gas stream from the reactor. For the reasons mentioned, a hybrid epoxy resin-silica coating was designed in this work that protects the copper surface against corrosion by H2S and at the same time withstands moderate temperatures. The coatings were obtained from three v/w ratios of TEOS / Resin (T/R): 0.64, 1.28 and 1.92, named as R1, R2 and R3 respectively. Silica was produced in situ by the Sol-Gel process. The coatings on copper substrates were obtained by dip-coating, annealed at 75 °C and treated at different temperatures for evaluating their resistance to temperature. The corrosion resistance of coatings to H2S was evaluated through ASTM D610−01 and ASTM D714−02 Standards. The structural characterization of the coatings was performed by FTIR, Streaming Potential, SEM and XPS. The R2 hybrid coating showed excellent resistance to temperature and H2S attack. From all the characterization carried out and taking into account the literature review, it is concluded that the Si-N bonds obtained via sol-gel in situ at relatively low temperatures (75 °C) contribute to the protection of copper foils against the effect of temperatures higher than 100 °C and to the protection of corrosion by H2S. Taking the R2 formulation, further experimentation will be carried out for coating the internal part of copper pipes of a solar heat exchanger prototype.