Development Of Two Environmentally Friendly Boiler Acid Cleaning Inhibitor

Acid cleaning inhibitor is an important additive on reducing corrosion of in the process of cleaning boiler. The current researches are focused on the exploitation of efficient, environment-friendly acid cleaning inhibitors for boilers.Following the concept of green chemistry, 2-mercapto benzimidazole was used as the main monomers of citric acid inhibitor.The modified from 2-phenyl-imidazolinequaternary ammonium salt as the main monomers of hydrochloric acid inhibitor. Efficient, environment-firendly compound corrosion inhibitors CA (citric inhibitor) and HA (hydrochloric acid) were screened by orthogonal tests. Both of them are environmentally friendly compound inhibitor for pickling power plant boiler.The optimal mixture compostion of CA was as follows: 0.08% (2-mercaptobenzimidazole) +0.12% (triethanolamine) +0.1% (potassium iodide) +0.024% (polyoxyethylene nonylphenyl ether) +0.04% (peregal ). Static etching 6 hours and citric acid concentration 5%of the medium when the temperature was 95±1℃, the static corrosion rate was 0.657g·m^-2·h^-1 and inhibition effciency was 98.76%. The optimal mixture compostion of HA was as follows: 0.1% (2-phenyl-imidazoline quaternary ammonium salt) + 0.08% (potassium iodide) + 0.12% (triethanolamine) + 0.03% (peregal ). When the temperature 52℃±1℃,static etching 6 hours and Hydrochloric acid concentration 5%, the static corrosion rate was 0.400g·m^-2·h^-1 and the inhibition effciency were 95.66%. A type of imidazolinylquaternary-ammonium-salt ( IMA ) was synthesized from Oleic acid and triethylenetetramine for hydrochloric pickling power plant boiler. Monomer concentration of 0.18%, the static corrosion rate was 0.42g·m^-2·h^-1 and the inhibition effciency were 95.43%.Employing weight loss method to research the corrosion inhibition properties of CA and HA. The results show that these two composite inhibitors have a good inhibitory performance even under the condition of low concentration. The composite inhibitors have a good corrosion resistance to Fe³⁺, when the Fe+3concentration 0 ¹000mg / L does not occur pitting.The CA, HA and IMA are mix-controlled inhibitors shown by Tafel polarization curves in electrochemical reaction process. The CA, HA and IMA come forth a"degradation"phenomenon are shown by Electrochemical Impedance Spectroscopy(EIS).The two composite inhibitors and IMA are controlled with the charge transfer. Wight loss method results are almost the same as electrochemical experimentaon inhibition effciency. The effciency formula was discovered from inhibition analysis of weight loss method. The CA, HA and IMA are geometric covering effect on the surface of the object, they satisfied with langmuir adsorption isotherm. A well-distributed, compacted corrosion film forms on the surface is shown by the SEM of the surface.